D4 NV Diamond - Instructional Physics Lab
Contents
1. This is a typical power used to excite the NVs in the diamond sample If you find less than 2 mW cycle power to the laser Galvo controlled mirrors Thorlabs GVS012 In order to locate NV centers in the diamond plate there is an xyz translation stage for course movement and galvo controlled mirrors for fine movement The mirrors mounted on motor controlled shafts are used to make small changes in the angle of the laser beam These are dc motors which receive power under control of the LabVIEW software at the rate of 1 25 degree Volt The Galvo Controls tab has buttons for increasing and decreasing the galvo voltages The Arrow keys on the computer keyboard are shortcuts for up down and right left Scanning microscope principle of operation As the galvo mirrors change the angle of the beam during a scan we require that the green and red beams remain colinear If this were not the case detection would be impossible since the red beam would miss the fiber for some range of the galvo mirrors travel To meet this requirement an optical trick 1s employed The lens in the figure refers to a composite of three actual lenses the pair of lenses downstream of the mirrors plus the objective The galvo mirrors and the sample plane are placed into the front and back focal planes of the composite lens respectively In this case the collimated portions of the beams remain colinear This telescope as well as one upstream of the galvo mirrors are2. www fas harvard edu phys191r References d4 Beveratos2001 pdf Phys Rev A 64 061802 R 2001 f A Beveratos et al Single photon quantum cryptography http www fas harvard edu phys191r References d4 Beveratos2002 pdf Phys Rev Lett 89 187901 2002 ft R Alleaume F Treussart G Messin Y Demeige J F Roch and A Beveratos R Brouri J P Poizat and P Grangier Experimental open air quantum key distribution with a single photon source http www fas harvard edu phys 19 1r References d4 Alleaume2004 pdf arXiv quant ph 0402110v1 2004 f A V Akimov A Mukherjee C L Yu D E Chang A S Zibrov P R Hemmer H Park and M D Lukin Generation of single optical plasmons in metallic nanowires coupled to quantum dots http www fas harvard edu phys191r References d4 Akimov2007 pdf Nature 450 402 406 15 November 2007 ft B Lounisa H A Bechtela D Gerionc P Alivisatosc and W E Moerner Photon antibunching in single cdse zns quantum dot fluorescence http www fas harvard edu phys191r References d4 Lounisa2000 pdf Chemical Physics Letters 329 399 404 October 2000 t T Gaebel et al Room temperature coherent coupling of single spins in diamond http www fas harvard edu phys 19 Ir References d4 Gaebel2006 pdf Nature Physics 2 408 2006 t N B Manson J P Harrison and M J Sellars The nitrogen vacancy center in diamond re visited http www fas harvard edu phys 1
3. 19 Ir References d4 vanOort1990 pdf Phys Rev B 42 8605 1990 37 A Gruber et al Scanning confocal optical microscopy and magnetic resonance on single defect centers http www fas harvard edu phys 19 Ir References d4 Gruber1997 pdf Science 276 2012 1997 38 1 N B Manson J P Harrison and M J Sellars The nitrogen vacancy center in diamond re visited http www fas harvard edu phys 19 Ir References d4 Manson2006 pdf arXiv cond mat 0601360v2 2006 39 1 L Childress J M Taylor A S S rensen and M D Lukin Fault tolerant quantum communication based on solid state photon emitters http www fas harvard edu phys 19 1r References d4 Childress2006 pdf Phys Rev Lett 96 070504 2006 40 F Jelezko et al Single spin states in a defect center resolved by optical spectroscopy http www fas harvard edu phys 19 Ir References d4 Jelezko2002 pdf App Phys Lett 81 2160 2002 41 t E T Charnock and T A Kennedy Combined optical and microwave approach for performing quantum spin operations on the nitrogen vacancy center in diamond http www fas harvard edu phys191r References d4 Charnock2001 pdf Phys Rev B 64 041201 R 2001 42 X F He N B Manson and P T H Fisk Paramagnetic resonance of photoexcited n v defects in diamond 11 hyperfine interaction with the n 14 nucleus http www fas harvard edu phys191r References d4 He1993 pdf Phys Rev B 47 8816 1993 43 M
4. Bragg reflection Two output beams are generated a zero order beam which is simply transmitted through the TeO _2 and a diffracted beam which is coupled to a fiber Green fiber A single mode fiber Thorlabs P1 630A FC 2 transmits light from the laser box to the confocal microscope box As currently configured Spring 2012 the output of the fiber is approximately 3 mW The mode field diameter of the fiber is 4 3 microns The fiber does not transmit 1064 nm light efficiently A Thorlabs F230FC B fiber collimator couples the free space laser beam into the fiber in the green laser box A Thorlabs CFC 8X A adjustable collimator is used at the other end of the fiber in the confocal microscope box The focal length of this collimator is 7 5 mm and the output beam waist diameter is 1 2 mm Neutral density filters Immediately downstream of the fiber coupler is a filter wheel housing neutral density filters Use these to attenuate the laser power Nominal values of the filters are given in the table For additional attenuation use the ND 1 0 filter mounted on a one inch post number on filter wheel attenuation log scale transmission linear scale oo OO Home Made Power Meter A photodiode mounted on a moveable post is used to measure the laser power leaving the fiber To measure the laser power place the photodiode downstream of the ND filters and switch the multimeter to dc current uA mps The calibration is 2 76 mW 275 microAmps
5. C3 operations one of the nearest neighbor carbon sites A energy levels consist of a single state which transforms into itself with no sign change under all symmetry operations A gt levels are also non degenerate but the state picks up a negative sign under reflections Finally E levels consist of a pair of states which transform into each other the way that the vectors 7 and y transform into each other under C3 symmetry operations For more details on C3 symmetry and group theory see Appendix of L Childress thesis 3 Electronic structure Although a number of efforts have been made to elucidate the electronic structure of the NV center from first principles l BILS it remains a topic of current research Experimentally it has been established that the NV center exists in two charge states NV and NV with the neutral state exhibiting a zero phonon line ZPL at 575nm and the singly charged state at 637nm 1 945 eV In this work we consider exclusively NV which is dominant in natural diamond and will refer to it simply as the NV center The electron configuration for the neutron NV center is a follows The five valence electrons of the nitrogen atom form covalent bonds with the three nearest neighbor carbon atoms while the remaining two form a lone pair that points in the direction of the neighboring carbon vacancy The three unpaired valence electrons of the carbon atoms adjacent to the carbon vacancy
6. O Scully and M S Zubairy Quantum Optics Cambridge University Press Cambridge UK 1997 44 M O Scully and M S Zubairy Quantum Optics Cambridge University Press Cambridge UK 1997 45 1 E L Hahn Spin Echoes http www fas harvard edu phys1911 References c4 hahn1950 pdf Phys Rev 80 580 1950 46 A Schweiger and G Jeschke Principles of pulse electron paramagnetic resonance Oxford University Press Oxford UK 2001 Introductory reading 1 The Diamond Age of Spintronics http www fas harvard edu phys 19 1r References d4 Awschalom2007 pdf David D Awschalom Ryan Epstein and Ronald Hanson Scientific American 297 4 84 October 2007 is a very general introduction to the subject for non specialists 2 Chapters 3 and 4 of Lillian Childress Ph D thesis contain a general overview of the subject and techniques as of 2006 available online http lukin physics harvard edu theses htm 3 Discussion of the level structure can be found in Properties of nitrogen vacancy centers in diamond the group theoretic approach http www fas harvard edu phys 19 1r References d4 Maze2011 pdf J R Maze A Gali E Togan Y Chu A Trifonov E Kaxiras and M D Lukin New J Phys 13 025025 2011 See also Jeronimo Maze s thesis http lukin physics harvard edu theses tm Bench notes National Instruments 6232 Multifunction ePCI card http www fas harvard edu phys 19 1r Bench_Notes D4 n1
7. an NV center prepared in the m state fluoresces more strongly than an NV center prepared in them 1 state 1541 Optically detected magnetic resonance in the NV center was observed first at low temperature in ensemble studies gt 1136 At room temperature this allows for efficient detection of the average spin population using resonant excitation at low temperature the effect is more pronounced and single shot readout is possible Specifically at room temperature the same mechanism which leads to optical spin polarization provides the means to optically detect the spin state Non resonant green excitation at e g 532 nm excites transitions from both them Qandm 1 ground state levels However because the intersystem crossing occurs primarily from the 7m excited state population in M 1 ground state undergoes fewer fluorescence cycles before shelving in the singlet state for around 300 ns The 7m states thus fluoresce less than the mM Q state with a difference of 20 40 37 38 39 Single spin magnetic resonance experiments The electron spin of an NV center can be polarized and measured using optical excitation as discussed above By tuning an applied microwave field in resonance with its transitions the spin can also be readily manipulated Although it is difficult to address a single spin with microwaves one can prepare and observe a single spin by confining the optical excitation volume to a sin
8. at a time and can therefore serve as a source of single photons In principle one could observe this effect by histogramming the time interval between different photons and examining the distribution close to zero delay If the source was a single quantum emitter the probability for a delay T between successive photons should vanish as 7 Owing to dead time effects for avalanche photodetectors such as the SPCMs we use it 1s impossible to make such a measurement directly To circumvent this problem it is necessary to divide the emitted photons between two detectors and measure the time interval T between a click in one detector and a click in the second detector In the limit of low count rates this measurement yields the probability of measuring a photon at time T conditional on detection of a photon at time which corresponds to a two time expectation value for the fluorescence intensity correlation function 1 7 1 Q Normalizing this quantity to the overall intensity J yields the second order correlation function for a stationary process I r I 0 2 Ideally we should observe g 0 0 for emission from a single quantum emitter whereas classical sources g t must have g 0 gt 1 7 Since a two photon state has g 9 observation of g 0 lt 1 Dis sufficient to show that the photons are emitted one at a time by a single quantum system The physical origin of vanishing coincidence probability fo
9. envelope such as Gaussian envelope e T ir which decays on a timescale 77 known as the electron spin dephasing time The dephasing time is the timescale on which the two spin states M and Mm accumulate random phase shifts relative to one another For the NV center these random phase shifts arise primarily from the effective magnetic field created by a complicated but slowly varying nuclear spin environment These frequency shifts can be eliminated by using a spin echo or Hahn echo technique l Tt can be used to extend the coherence time and to gain addition insights into spin dynamics Spin echo consists of the sequence Ti D a T T T mj 2 see Fig SA where 7T represents a microwave pulse of sufficient duration to flip the electron spin fromm Utom 1 and 7 y are durations of free precession intervals As with the Ramsey sequence the Hahn sequence begins by preparing a superposition of electron spin states 1 2 0 i 1 using a Tj 2 microwave pulse This superposition precesses freely for a time T so that for example the 1 component picks up a phase shift ot relative to the O component yielding 1 2 10 je 1 The zt pulse in the middle of the spin echo sequence flips the spin resulting in the state 1 2 il 1 jet 0 l Assuming that the environment has not changed since the first free precession interval the 1 component will pick up the phase during the second free pre
10. frequency of microwave excitation appropriate for pulsed experiments However the lan hyperfine structure illustrates that CW measurements can also be useful for determining interaction strengths between the NV electron spin and other nearby spins Pulsed microwave experiments Continuous wave spectroscopy provides a means to measure the energy levels of the NV spin system To observe the spin dynamics we must move to the time domain and apply pulses of resonant microwaves The excitation sequence for pulsed microwave experiments is illustrated in Fig 5A All experiments begin with electron spin polarization and end with electron spin measurement both of which are accomplished using 532 nm excitation In between different microwave pulse sequences can be applied to manipulate the electron spin Rabi oscillations In a small applied magnetic field the m tom spin transition of the NV center constitutes an effective two level system Driving this transition with resonant microwave excitation will thus induce population oscillations between the ground mM Q and excited m states these are known as Rabi oscillations 7 To observe Rabi nutations we drive the transition with a resonant microwave pulse of varying duration and measure the population remaining in 7m Fig 5B shows a typical Rabi signal For resonant microwave excitation Rabi oscillations correspond to complete state transfer between M U and Me Th
11. of similar intensity We can position the focus on top of one of the bright spots and examine its fluorescence Several observations can be made to verify that the signal originates from the NV centers First the NV centers are photo stable 1 e fluorescence should not blink or disappear Second photon count rate associated with single atom emission should undergo saturation as the intensity of the excitation laser is increased Assuming that the the excited state lifetime of NV centers is known or could be found from independent measurements as discussed below the saturation curve can be used for calibration of the excitation rate for a given laser intensity Make a simple model to predict a fractional form of saturation Using this model and saturation measurements you can find the correspondence between the excitation rate and a laser power for any given NV center To verify that the observed signals are from single quantum emitters photon correlation measurements can be used One important quantum mechanical property of the radiation field is its statistics The radiation from thermal sources like a lamp or coherent sources like laser is characterized by a distribution of photon numbers A sequence of measurements on nominally identical weak pulses produced by such sources will reveal fluctuations in photon number associated with quantum nature of such pulses In contrast a single atom emitter is incapable of producing more than one photon
12. provide input pulses for the TimeHarp inputs SYNC and START The SYNC input requires a fast negative pulse to trigger a measurement A positive pulse in the range of 50 1500 mV at the START input stops the measurement After a measurement the time interval is added to a histogram of up to 4096 bins The TimeHarp card has an incredibly small time resolution of 40 ps However the dead time associated with each event is 350 ns Given the limitation of dead time it is only possible to measure g T when the count rate is low compared to the histogram bin duration Is this approximation valid for typical experimental parameters Suppose that the probability of detecting a photon in any particular time bin after a SYNC pulse is small In this case most bins will have zero counts and one particular bin y will receive one count and stop the measurement The SYNC pulse corresponds to J 0 Land F T 0 for most time intervals 7 T 1 Thus g 7 apart from the normalizing factor I y Repeating the measurement many times is necessary to build up a histogram with adequate statistics The maximum number of TimeHarp histogram bins is 4096 We wish to observe g lt 1 ona time scale smaller than the dead time of both the APDs and the TimeHarp To circumvent the APD dead time we split the signal into two APDs To circumvent the TimeHarp dead time a length of coaxial cable is inserted into the SYNC channel moving the featur
13. separated by a seg os en variable delay Minimum Maximum and Step set the range and increment of the delay See the figure at left The 7 2 pulse should be set to one 2 i quarter of the Rabi period 7 time is not used t 0 t t ta2 time Hahn Echo Microwave pulse sequence for Ramsey oscillation HAHN ECHO The Hahn echo p ulse m lope sequence is a 7 2 it ST i pulse followed by a m pulse followed by i i i another 7 2 pulse teO tetera te 2tetsetal time The delay between Microwave pulse sequence for Hahn echo pulses is the same and Minimum Maximum and Step set the range and increment of this delay See the figure at left The 7 and 7 2 pulses should be set to one quarter and one half the Rabi period respectively Readout In order to measure the probability of finding the NV center in the m Q state a pulse of green light is used Refer to the figure at right TReadOur 18 the nominal start SOU time t 0 for readout TReadOut Maximum ns 1000ns lt t green length gt for Rabi and Ramsey pulse sequences TReadOut 2 Se Maximum ns 1000ns for the Hahn Echo pulse sequence O O E Manat The green light actually comes on earlier by an amount ms T4om Since the Acousto Optic Modulator has a finite rise te TRO TCictat i i i i te Taos TCictat i time unlike the square pulse shown te TReadQut TAOM The first counter window defined by parameters Green laser pulse and coun
14. techniques Recently there has been renewed interest in the NV center as a physical system for quantum information science in the solid state The NV center is an attractive quantum bit qubit candidate because it behaves like an atom trapped in the diamond lattice it has strong optical transitions and an electron spin degree of freedom In what follows we consider the basic structure of the NV center and describe experimental techniques used to probe its spin and optical properties Structure of the NV center Physical structure The NV center is formed by a missing carbon atom adjacent to a substitutional nitrogen impurity in the face centered cubic fcc diamond lattice see Fig 1A The physical structure of this defect and the symmetries associated with it determine the nature of its electronic states and the dipole allowed transitions between them see Fig 2 The symmetry properties of the NV center provide insight into the nature of its electronic states Unlike atoms in free space whose electronic states are governed by their rotational invariance the NV center exhibits C3 symmetry Figure 1 A The nitrogen vacancy center in diamond B The symmetry operations for the C3 group include rotations by 27n 3 around the vertical symmetry axis and reflections in the three as illustrated in Fig 1B Electronic states are thus planes containing the vertical symmetry axis and characterized by how they transform under
15. 5 dBm The maximum amplifier output is 13 Watts The instrument bandwidth is from 2800 to 3000 MHz There are four analog inputs and three green indicator LEDs on the front panel of the microwave synthesizer INPUTS OSC EXT accepts an external clock signal It is not normally used GATE is used during pulse experiments such as Rabi oscillation Input is accepted from PBO of the SpinCore ESR PRO 400 SWEEP is a pulse input from the NI6323 Userl B which starts a microwave sweep ATTEN requires analog voltages from zero to 5 Volts from the NI6323 analog output AOI A INDICATORS Output active lights when the microwave source 1s providing output nitialize is on briefly when LabVIEW initializes communication Oscillator Locked should light at all times when the unit is in use This indicates that the microwave frequency is stable A schematic diagram of the microwave source is available in the bench notes An antenna and microwave detector Telonic XD 23E can also be used to measure radiated microwave power in arbitrary units Electronics block diagram For reference a diagram showing all electrical connections is included in the bench notes An AutoCAD drawing with full resolution is available on the NV lab computer SpinCore Technologies PulseBlaster ESR PRO 400 PCI Pulse Generator Board The pulse generator PCI card generates TTL pulses used in three separate applications Output number 0 is a trigger pulse for the micr
16. 6323 pdf National Instruments BNC 2090A Breakout Box http www fas harvard edu phys191r Bench_Notes D4 ni_bnce2090a pdf Dell Optiplex 980 Technical Guide http www fas harvard edu phys 19 1r Bench_Notes optiplex 980 tech guide pdf Crystal Technology Acousto Optic Modulator Principles of Operation http www fas harvard edu phys191r Bench_Notes D4 AO_Modulator3000_appnote pdf Crystal Technology AOMO 3080 125 Acousto Optic Modulator Spec Sheet http www fas harvard edu phys191r Bench_Notes D4 AOM pdf Crystal Technology AODR 1080AF DIFO 1 0 Acousto Optic Modulator Driver http www fas harvard edu phys191r Bench_Notes D4 AOM_driver pdf Crystal Technology AODR 1080AF DIFO 1 0 Acousto Optic Modulator Driver Test Sheet http www fas harvard edu phys191r Bench_Notes D4 AOM_driver_test pdf Perkin Elmer SPCM AQR 14 FC Single Photon Counting Module http www fas harvard edu phys 19 1r Bench_Notes D4 SPCMAQR pdf PicoQuant TimeHarp 200 PCI board for Time Correlated Single Photon Counting http www picoquant com products timeharp200 timeharp200 htm TimeHarp 200 Spec Sheet pdf http www fas harvard edu phys191r Bench_Notes D4 TimeHarp200 pdf TimeHarp 200 User Manual large pdf http www fas harvard edu phys191r Bench_Notes D4 timeharp200_user pdf SpinCore Technologies PulseBlasterESR PRO 400 PCI Pulse Generator Board http www fas harvard edu phys191r Bench_Notes D4 PBESR Pro_Manual pdf Niko
17. 9 1r References d4 Manson2006 pdf arXiv cond mat 0601360v2 2006 t J Wrachtrup and F Jelezko Quantum information processing in diamond http www fas harvard edu phys 19 Ir References d4 Wrachtrup2006 pdf J Phys Condens Matter 18 S807 2006 t The model presented here is based on the recent theoretical work Manson 2006 which provides an adequate explanation for most observations According to this model transitions between the triplet and singlet states occur via the spin orbit interaction which mixes states of the same irreducible representation The excited state intersystem crossing favors the 72 1 states because in the absence of strain there is an A excited state with Dr S character Conversely the decay from the singlet leads to the A ground state which has spin projection Ms Q f A Gruber et al Scanning confocal optical microscopy and magnetic resonance on single defect centers http www fas harvard edu phys19Ir References d4 Gruber1997 pdf Science 276 2012 1997 t E van Oort N B Manson and M Glasbeek Optically detected spin coherence of the diamond n v centre in its triplet ground state http www fas harvard edu phys191r References d4 vanOort1988 pdf J Phys C Solid State Phys 21 4385 1988 t E van Oort P Stroomer and M Glasbeek Low field optically detected magnetic resonance of a coupled triplet doublet defect pair in diamond http www fas harvard edu phys
18. C connectors LabVIEW program NV_191 vi courtesy of Mike Goldman A LabVIEW program written by the Lukin group controls the experiment and acquires data Referring to the figure zones A through G are a collection of controls and indicators Data files can be saved using the controls in the lower right Zone A is a map showing the intensity of red light emitted by the sample Scanning an appropriate area is important since you may not see NVs if the resolution is too low Typical scan range is 0 2 V in X and Y which corresponds to about 8 microns As of summer 2012 bright NVs can be seen in the range X 0 1 V 0 1 V Y 04 V 0 2 V This is for micrometer settings X 6 318 mm Y 7 555 mm and Z 6 023 mm You can look anywhere in the Front panel of NV LabVIEW program sample for NVs To expedite your experiment consider using established parameters Zone B is a data window which varies from tab to tab The Counter Readout tab is shown Zone C selects the active set of controls The box below Zone C shows controls for Galvo Positioning PicoHarp Microwave Pulse Experiment etc The box above Zone D contains controls for the Galvo Scan The buttons below are start and stop controls for Galvo Scan Counter NV lock Microwave scan Picoharp and Pulse Experiments Zone E is the Optimize button important enough to have its own zone The stability of the NV count rate is usually good enough to make measurements
19. D 4 Nitrogen Vacancy Centers in Diamond From Physics 191r contributors M Lukin S Zibrov M Goldman 2012 N V Centers in Diamond Sept 2012 pdf File Nvlab 4 pdf Contents Probing amp control of single quantum systems in diamond 2 Summary 3 Learning Goals 4 Introduction 5 Structure of the NV center 5 1 Physical structure a 5 2 Electronic structure 6 Experiment 7 Isolation of single NV centers single photon source Spin properties of the NV center 8 1 Optically induced spin polarization 8 2 Spin dependent fluorescence 9 Single spin magnetic resonance experiments 9 1 Continuous wave experiments a 9 2 Pulsed microwave experiments 9 2 1 Rabi oscillations 9 2 2 Ramsey fringes and spin echo 10 Photos 11 Apparatus 11 1 Confocal Microscope 11 1 1 Laser 11 1 2 Acousto optic modulator Crystal Technology 3080 125 controller 1O80AF DIFO 1 0 11 1 3 Green fiber 11 1 4 Neutral density filters 11 1 5 Home Made Power Meter 11 1 6 Galvo controlled mirrors Thorlabs GVSO12 11 1 7 Scanning microscope principle of operation 11 1 8 Objective Nikon MRHO1902 CFI Plan Fluor 100x Oil Immersion 11 1 9 Sample 11 1 10 Translation stage Newport 562 X YZ 11 1 11 Dichroic beamsplitter Semrock LMO01 552 25 11 1 12 Red detection 11 1 13 Single Photon Counting Modules Perkin Elmer SPCM AQR 14 FC 11 2 National Instruments PCIe 6323 X Series Multifunction ePCI card 11 3 LabVIEW program NV_191 vi 11 4 Pi
20. ate lifetime Spin properties of the NV center While discussing the electronic structure of the NV center we have already touched upon the existence of an S 1 spin degree of freedom in the ground and excited states In this section we will consider in greater detail the interplay between optical transitions and the spin degree of freedom Optically induced spin polarization Early experiments established that the NV center spin shows a finite polarization under optical illumination with green light see Fig 2 Over the years it has been determined that optical excitation causes the ground Mls state to become occupied with high probability and recent measurements indicates that nearly full polarization may occur l gt 0 Nevertheless the precise mechanism for optically induced spin polarization is still a topic of active research 1 Spin polarization originates due to existence of a singlet electronic state whose energy level lies between the ground and excited state triplets see Fig 2 Transitions into this singlet state occur primarily from Mm 1 states whereas decay from the singlet leads primarily to the m Q ground state gt 9 If the remaining optical transitions are spin preserving this mechanism should fully polarize the NV center into the m QO ground state Spin dependent fluorescence Most current research on the NV center in diamond relies on optical detection of its ground state spin Experimentally
21. cession interval leaving the system in the state 1 2 ie 1 jet 0 When the two wait times are precisely equal y y the random phase shift factors out so the final mj 2 pulse puts all of the opulation back into When the wait times are unequal the Hahn sequence behaves like a Ramsey sequence pop q with a delay y 7 Spin echo 1s widely used in bulk electron spin resonance ESR experiments to study interactions and determine the structure of complex molecules Likewise spin echo spectroscopy provides a useful tool for understanding the complex mesoscopic environment of a single NV center by observing the spin echo signal peak y 7 we can decouple spin dynamics from low frequency environment extend its coherent evolution and can indirectly glean details about the environment itself Finally spin echo and other related decoupling techniques constitute an important tool for extending coherence times of spin qubits Applications of such techniques ranging from quantum computation to nanoscale magnetometry are at the forefront of the modern research Photos Confocal microscope Apparatus Confocal Microscope A confocal microscope illuminates a small region of a sample with a focussed laser beam and fluorescence is detected from the same region The beam scans across the sample by means of a 2D rotating mirror galvanometer A schematic diagram of the optics is given below Three separa
22. chosen so that the beam diameter matches the size of the objective s rear aperture to make the sharpest possible focus A Samp Plane Gale Miro Principle of confocal microscope The Galvo mirror and the sample plane are placed into the front and back focal planes of the lens respectively In such a case the excitation path green and collection path red can be identical Objective Nikon MRH01902 CFI Plan Fluor 100x Oil Immersion The Nikon objective has magnification 100x and working distance of 0 2 mm The numerical aperture is 1 30 and the effective focal length is 2 mm The field of view is 0 18 mm The immersion oil has high viscosity and normally does not need to be refreshed between experimental runs Sample The sample is a type Ila high purity diamond selected for low nitrogen content It is a natural diamond originating in the Ural Mountains The sample is epoxied to a silicon substrate Silicon is chosen because it absorbs approximately 70 of the incident green light and does not emit red fluorescence Under normal operation it is not advisable to remove the sample for viewing A photo is included in the Experiment section above Translation stage Newport 562 X YZ The sample is mounted on a stainless steel translation stage The translation stage is used for coarse positioning during alignment Under normal operation it is not advisable to move the translation stage However fine control of focuss
23. coQuant TimeHarp 200 PCI board for Time Correlated Single Photon Counting 11 5 Microwave Source and Amplifier 11 5 1 INPUTS 11 5 2 INDICATORS 11 6 Electronics block diagram 11 7 SpinCore Technologies PulseBlaster ESR PRO 400 PCI Pulse Generator Board 11 8 Pulse Experiments 11 8 1 Rabi 11 8 2 Ramsey 11 8 3 Hahn Echo 11 8 4 Readout 12 References 13 Introductory reading 14 Bench notes 15 Appendix microwave source calibration Probing amp control of single quantum systems in diamond Summary This experiment explores control over individual quantum objects such as single photons and single electronic spins It utilizes a confocal microscope to isolate and manipulate individual atom like impurity in a diamond crystal Optical excitation of this isolated impurity is used to study a very unusual light source in which single photons are emitted one at a time Optical and microwave radiation is then used to control and manipulate the electronic spin state associated with the single impurity Experimental techniques and methods introduced in this experiment form the basis for an exciting modern research direction involving the applications of individual atoms and atom like systems for quantum information processing communication and metrology Learning Goals Use a confocal microscope to observe nitrogen vacancy centers in diamond Measure the correlation function for light emitted by a single n v center to observe an
24. d rejection in our setup the single mode fiber replaces the pinhole Ideally this constitutes mode matching between the mode collected by the objective from the NV center point source and the mode of the fiber The fiber is itself acts as a beamsplitter whose two outputs are connected to fiber coupled single photon counting modules SPCMs Perkin Elmer Overall the collection efficiency for fluorescence from the sample is just under 1 To apply strong microwaves to the NV center the sample is mounted on a circuit board with a microwave stripline leading to and away from it A 20 um copper wire placed over the sample is soldered to the striplines By considering NV centers close to the wire we can achieve large amplitudes for the oscillating magnetic field with modest microwave power through the wire A static applied magnetic field can be varied using a permanent magnet mounted on a three axis translational stage To measure the magnetic field a three axis Hall sensor is mounted close to the sample In addition the NV center itself can be used as a magnetometer to measure the component of the magnetic field along the NV axis Isolation of single NV centers single photon source The small excitation and detection volume of our confocal microscope combined with the low concentration of NV centers in the sample allows us to image single NV centers Scanning the focal spot of the microscope over the sample reveals scattered bright spots
25. df Phys Rev A 64 061802 R 2001 t Ph Tamarat et al Stark shift control of single optical centers in diamond http www fas harvard edu phys191r References d4 Tamarat2006 pdf Phys Rev Lett 97 083002 2006 F Jelezko et al Observation of coherent oscillation of a single nuclear spin and realization of a two qubit conditional quantum gate http www fas harvard edu phys1911r References d4 Jelezko2004 pdf Phys Rev Lett 93 130501 2004 t Wikipedia Confocal microscopy http en wikipedia org wiki Confocal_microscopy t R J Epstein F Mendoza Y K Kato and D D Awschalom Anisotropic interactions of a single spin Dz AI 24 Zs 26 Dil 28 29 30 31 a2 33 34 35 36 and dark spin spectroscopy in diamond http www fas harvard edu phys 19 1r References d4 Epstein2005 pdf Nature Physics 1 94 2005 f Leonard Mandel and Emil Wolf Optical Coherence and Quantum Optics Cambridge University Press Berlin 1995 ft Roy J Glauber Nobel lecture One hundred years of light quanta http www nobelprize org nobel_prizes physics laureates 2005 glauber lecture html f C Kurtsiefer S Mayer P Zarda and H Weinfurter Stable solid state source of single photons http www fas harvard edu phys 19 1r References d4 Kurtsiefer2000 pdf Phys Rev Lett 85 290 2000 f A Beveratos et al Nonclassical radiation from diamond nanocrystals http
26. e 7 y plane is set by the phase of the microwave excitation For a single pulse this phase does not matter it could equally well be incorporated into a redefinition of 1 but composite pulse sequences often make use of shifts in the microwave phase As an example a pulse A of duration f followed by a 9 degree phase shifted pulse B of duration f p would correspond to rotating the spin by f 4 around the 7 axis followed by a rotation by f p around the y axis Ramsey fringes and spin echo Rabi nutations correspond to driven spin dynamics We can also observe the free undriven spin dynamics by generating a superposition of the spin eigenstates m Qandm 1 letting it evolve freely and then converting the phase between the two eigenstates into a measurable population difference This is accomplished 44 using a Ramsey technique which consists of the microwave pulse sequence 7 2 T Tj 2 as illustrated in the inset to Fig 5C For a simple two level system the Ramsey sequence leads to population oscillations with a frequency equal to the microwave detuning Because of the 14N hyperfine structure we observe a more complex signal from three independent two level systems These three signals beat together producing the complicated pattern shown in Fig 5C The data can be modeled with three superposed cosines corresponding to the three hyperfine transitions The fit to the Ramsey data should also include an overall
27. e of interest to a time much longer than the dead time Since the APDs are nominally identical in principle the delay could be in either channel The LabVIEW Controls to View Picoharp Settings tab contains six controls Typical parameters are mentioned in square brackets Resolution 64 ps is the bin size that the TimeHarp card uses to acquire data Acquisition time 1000 ms is the total time available for a single acquisition The actual time required for a single measurement is determined by the resolution and the number of bins Many measurements can be added to improve signal to noise ratio Channel 0 level 100 mV Channel 1 level 50 mV Channel 0 zero X 5 mV Channel 1 zero X 5 mV The Counter Model control must be set to TimeHarp for proper functioning of the TimeHarp card However the word PicoHarp is used in the Zone F tab name interchangeably with TimeHarp For technical reasons the Resolution indicator in Zone F reads differently than the Zone C control Saving data from the TimeHarp card is done automatically if the Save Data switch is turned on Data can not be saved after a run completes Microwave Source and Amplifier The microwave source is controlled by LabVIEW through a USB interface COM3 as well as by analog output AO1 A The analog voltage activates two MiniCircuits RVA33 attenuators The attenuator control in the LabVIEW program give the output of the microwave synthesizer in dBm The amplifier gain is 4
28. ef and S C Rand Electronic structure of the n v center in diamond Theory http www fas harvard edu phys 19 1r References d4 Lenef1996b pdf Phys Rev B 53 13441 1996 and A Lenef et al Electronic structure of the n v center in diamond Experiment http www fas harvard edu phys 19 1r References d4 Lenef1996a pdf Phys Rev B 53 13427 1996 J P D Martin Fine structure of excited e 3 state in nitrogen vacancy centre of diamond J Lumin 81 237 1999 1 N B Manson J P Harrison and M J Sellars The nitrogen vacancy center in diamond re visited http www fas harvard edu phys 19 1r References d4 Manson2006 pdf arXiv cond mat 0601360v2 2006 T Gaebel et al Photochromism in single nitrogen vacancy defect in diamond http www fas harvard edu phys 19 Ir References d4 Gaebel2006b pdf Appl Phys B Lasers and Optics 82 243 2006 f N R S Reddy N B Manson and E R Krausz 2 laser spectral hole burning in a color center in diamond J Lumin 38 46 1987 D A Redman S Brown R H Sands and S C Rand Spin dynamics and electronic states of nv centers in diamond by epr and four wave mixing spectroscopy http www fas harvard edu phys 19 Ir References d4 Redman1991 pdf Phys Rev Lett 67 3420 1991 t J H H Loubser and J A van Wyk Electron spin resonance in the study of diamond http www fas harvard edu phys 19 1r References d4 Loubser1978 pdf Rep Pr
29. electronics pdf Block diagram of electronics pdf Block diagram of microwave source png 2 4 18 77 Appendix microwave source calibration Evaluating MiniCircuits RVA33 attenuator two in series with IFR spectrum analyzer at 2 0 GHz 0 dBm source Measured return signal with DUT replaced by SMA barrel is 3 58 dBm Measured return signal with DUT in place powered with 5 0 V various control voltages Retrieved from https coursewikis fas harvard edu phys191r D 4_Nitrogen Vacancy_Centers_in_Diamond This page was last modified on 28 February 2013 at 16 19
30. for several minutes but there is a tendency to drift Small changes in position caused by temperature fluctuation and other factors cause the signal to change over time Optimize is a routine which scans a small range of X and Y looking for maximum signal Optimize before starting each data run NV lock is automatic Optimizing Zone F is a set of tabs Counter Readout is a graph of total counts sum of two APDs as a function of time NV Tracking Fits shows the fits computed by the Optimize routine NV Tracking History gives several ways of monitoring the position of an NV MW Scan Result is a graph of count rate synchronized with microwave sweep Many sweeps are averaged and the result displayed MW Scan History is a color representation of every microwave sweep in the series of averages Pulse Experiment controls pulsed ESR experiments PicoHarp displays the result of g2 correlation measurements Zone G activates the acousto optic modulator coupling the green laser light into the fiber which in turn illuminates the confocal microscope PicoQuant TimeHarp 200 PCI board for Time Correlated Single Photon Counting As discussed above in section 4 we wish to use the TimeHarp 200 to measure the second order correlation function for the photons emitted by an NV center The TimeHarp card measures and digitizes the time interval between two photon events Two APDs each receive approximately 50 of the NV photons and
31. gle NV center These ingredients provide a straightforward means to prepare manipulate and measure a single electronic spin in the solid state at room temperature 7 The experiments involving the NV electron spin can be roughly divided into continuous wave CW and pulsed experiments In both cases we isolate a single spin using confocal microscopy and apply microwaves to it using a 20 um copper wire drawn over the surface of the sample Fig 4 Continuous wave experiments For continuous wave CW measurements microwave and optical excitation are applied at constant power to the NV center and the fluorescence intensity into the phonon sideband is measured as a function of microwave frequency The continuous 532 nm excitation polarizes the electron spin into the brighter m Q state when the microwave frequency is resonant with one of the spin transitions M Q m 1 the population is redistributed between the two levels and the fluorescence level decreases In the absence of an applied magnetic field the electron spin resonance ESR signal occurs at 2 87 GHz while in a finite magnetic field the two transitions are shifted apart by Mls 2 8 MHz Gauss In this experiment you will observe and explore single spin ESR signal Explore experimentally and explain how does this signal depend on applied microwave and optical power Make a model for power dependance and check its consistency with excitation rate measurements Explore
32. how the signal changes with applied magnetic field Once the signal is optimized close examination of a single M 0 M transition may reveal hyperfine structure associated with the nitrogen forming the NV center Some NV centers have a structure that makes the hyperfine splitting more obvious The f 1 l4 nuclear spin has a hyperfine structure which is governed by the Hamiltonian fap e cone a ae er nce duces HN Aw po ki 4 AS S_ Io E Sit P 0 1 where I N is the nitrogen nuclear spin and is the NV center electron spin A strong quadrupole interaction splits the my states off from the my 0 state by P5 MHz 2 effectively freezing the orientation of the nitrogen nuclear spin for magnetic fields lt 1 Tesla In addition the l4 nuclear spin interacts with the electron spin so that in the electron spin excited state 7m the my states are split from the m y QO state by P 4 A sal and P A us Since the electron spin resonance transitions cannot change the nuclear spin state the three allowed transitions are separated by 4 WV oy 2 2 MHz To resolve hyperfine structure you will need to turn down the optical and microwave power such that the resulting linewidths are below 4 ur For laser power of a few milliWatts a factor of 100 attenuation is typical microwave power has to be reduced in tandem These CW measurements served primarily as a means to calibrate the
33. ing is accomplished with a piezoelectric transducer mounted under the vertical micrometer screw Voltage is applied to the PZT by a Thorlabs MDT693A piezo controller which in turn receives an input control signal from the NI 6323 under control of LabVIEW The emph Galvo Controls tab has buttons for increasing and decreasing the PZT voltage The Page Up Page Down keys are shortcuts for the Shallower Deeper Dichroic beamsplitter Semrock LM01 552 25 The dichroic beamsplitter reflects green and transmits red The beamsplitter separates the red detection beam from the green excitation beam Red detection In order to reject green light scattered from the sample a long pass filter Omega Optical 3RD600LP is placed downstream of the dichroic beamsplitter The transmission of the dichroic beamsplitter 1s one percent at 532 nm whereas the transmission of the long pass filter is only 10 4 6 whereas the red transmission is greater than 80 The red light is focused by a second microscope objective an Olympus 20X objective with NA 0 4 The working distance is 1 2 mm and the focal length is 9 mm A New Focus 9091 fiber coupler has fine controls for the position and angle of a fiber The fiber connector Summer 2012 is slightly flaky You may find the fiber tied down with cable ties for this reason This fiber leads to a Thorlabs FC632 50B FC 50 50 beam splitter which delivers red photons to the two detectors Single Photon Counting Modules Perkin Elme
34. is allows us to calibrate our measurement tool in terms of the population P in the m Q state As shown in Fig 5B we can identify the minimum in fluorescence with p Q and the maximum with p 1 For weak or off resonant microwave fields one employs a more careful analysis which fits the data to a multi level model including all of the hyperfine structure associated with the l4N nuclear spin and any other nearby spins In either case we can present data from more complicated pulsed experiments in units of Mls UO population p obtained from fits to Rabi nutations observed under the same conditions The frequency of the Rabi nutations depends on the j Irw FOr a given microwave power we observe Rabi nutations to calibrate the pulse length required to flip the spin from m to Mle this is known as a 7 pulse because it corresponds to half of the Rabi period Shorter and longer pulses create superpositions of the spin eigenstates in particular a microwave f pulse i e of duration t 0 Q sends the Ms O state 0 into the superposition microwave power Iyw as Q ox y cos 0 sin 0 1 This corresponds to rotating the Figure 5 Pulsed electron spin resonance Pulse effective spin 1 2 system 0 1 by about an axis in sequence for Rabi oscillation a and Ramsey the 7 y plane The relative phase of the two components sequence b experiments or equivalently the orientation of the axis in th
35. n Objective Specifications http www nikoninstruments com Products Optics Objectives Fluor Objectives CFI Plan Fluor Series specifications Semrock LMO1 552 25 dichroic filter http www fas harvard edu phys 19 1r Bench_Notes D4 semrockLM0O1 552 25 pdf Omega Optical 3RD600LP long pass filter http www fas harvard edu phys191r Bench_Notes D4 omega_3rd600Ip pdf Newport 562 X YZ Translation Stage Interferometer Test Sheet http www fas harvard edu phys191r Bench_Notes D4 newport_562xyz pdf Thorlabs FC632 50B FC single mode 50 50 standard fused fiber optic coupler spec sheet http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_FC632_50B_FC pdf Thorlabs FC632 50B FC single mode 50 50 standard fused fiber optic coupler test sheet http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_sm600_test pdf Thorlabs P1 630A FC 2 single mode fiber patch cable http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_P1 630A FC 2 pdf Thorlabs F230FC B Fiber Collimation Package http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_F230FC B pdf Thorlabs MDT 693 Piezo Driver http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_mdt693a pdf Thorlabs Dual Axis Scanning Galvanometer Power Supply http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_gps011 pdf Thorlabs Dual Axis Scanning Galvanometer System http www fas harvard edu phys191r Bench_Notes D4 Thorlabs_gvs012 pdf File Nv
36. oadband PSB fluorescence is collected Experiment Many of the early experiments on NV centers looked at ensemble properties averaging over orientation strain and other inhomogeneities Recently confocal microscopy techniques have enabled examination of single NV centers 1 gt permitting a variety of new experiments studying photon correlation statistics 19H single optical transitions coupling to nearby spins and other effects difficult or impossible to observe in ensemble studies To study NV centers in diamond we use a scanning confocal microscope incorporating magnetic field control and microwave coupling The confocal microscope uses point illumination and detection along the identical path in order to increase the signal to noise ratio The essential features of the apparatus are shown in Fig 3 The sample we use is a type IIa diamond specially selected for low nitrogen content lt ppm This low nitrogen content is critical for observing coherent processes of the NV spin degree of freedom because the electron spin associated with nitrogen donors interacts strongly with the NV center spin In the experiment we study the NV centers that occur naturally in bulk diamond Our measurements rely on optically exciting a single NV within the sample and detecting its fluorescence Excitation into the vibronic sideband of the NV center is performed using a 532 nm doubled Y AG laser The excitation beam pa
37. occupy molecular orbitals Two of these electrons occupy the lowest energy orbital with antiparallel spins while the third spin is unpaired The NV center is paramagnetic with spin S 1 2 The charged NV center is formed by addition of one more electron which combines with the unpaired electron of NV to form a spin S 1 The NV center has C3 symmetry with the ZPL emission band associated with an A to E dipole transition Hole burning electron spin resonance ESR ra optically detected magnetic resonance ODMR l Il and Raman heterodyne experiments have established that the ground electronic state is a spin triplet AS This triplet is itself split by spin spin interactions yielding one state with Mm U with A character and two M 1 states with E character which are 2 87 GHz higher in energy Together with the 637nm ZPL the 2 87 GHz zero field ground state splitting allows identification of a defect in diamond as an NV center In addition to the discrete electronic excited states which contribute to the ZPL there are a continuum of vibronic excited states which appear at higher frequencies in absorption and lower frequencies in emission When the Figure 2 a The electronic structure of the NV center The orbital states are indicated on the left hand side and the spin spin splitting of the ground state is indicated on the right hand side After accounting for all spin orbit spin spin and strain per
38. og Phys 41 1201 1978 t E van Oort N B Manson and M Glasbeek Optically detected spin coherence of the diamond n v centre in its triplet ground state http www fas harvard edu phys191r References d4 vanOort1988 pdf J Phys C Solid State Phys 21 4385 1988 t N B Manson X F He and P T H Fisk Raman heterodyne detected electron nuclear double resonance measurements of the nitrogen vacancy center in diamond http www fas harvard edu phys 19 1r References d4 Manson1990 pdf Opt Lett 15 1094 1990 t N B Manson J P Harrison and M J Sellars The nitrogen vacancy center in diamond re visited http www fas harvard edu phys 19 1r References d4 Manson2006 pdf arXiv cond mat 0601360v2 2006 F Jelezko et al Spectroscopy of single n v centers in diamond http www fas harvard edu phys 19 Ir References d4 Jelezko2001 pdf Single Mol 2 255 2001 f A Gruber et al Scanning confocal optical microscopy and magnetic resonance on single defect centers http www fas harvard edu phys 19 Ir References d4 Gruber1997 pdf Science 276 2012 1997 f C Kurtsiefer S Mayer P Zarda and H Weinfurter Stable solid state source of single photons http www fas harvard edu phys 19 1r References d4 Kurtsiefer2000 pdf Phys Rev Lett 85 290 2000 f A Beveratos et al Nonclassical radiation from diamond nanocrystals http www fas harvard edu phys191r References d4 Beveratos2001 p
39. owave generator Output number triggers the acousto optic modulator Output number 3 triggers microwave pulses for the Rabi and Ramsey experiments The minimum pulse duration is 2 5 ns All outputs have 50 ohm impedance Pulse Experiments After completing the Continuous Wave ESR experiment with external magnetic field one is in a position to carry out experiments with pulsed microwaves Select one of the resonances and fix the microwave frequency to match it Turn OFF the microwaves Set appropriate parameters in the Pulse Experiment control window pictured at right Details of the pulse sequences are given below All pulse experiments have to be repeated a large number of times to accumulate adequate statistics Rabi Rabi oscillations correspond to eres aD varying probability for the NV center to be found in the mm Qor Ms spin states A single resonant microwave pulse of variable eee EM duration is applied and a pulse of Microwave green light reads out the NV center pulse sequence spin state for Rabi oscillation The scan parameters Minimum Maximum and Step set the range and increment of the microwave pulse duration m and 7 2 times are not used A typical value for Maximum is 5000 ns when the microwave power is 21 dB One can measure the Rabi LabVIEW control panel for pulse settings period as a function of microwave power Ramsey RAMSEY The Ramsey pulse sequence is a pair of 7 2 pulses
40. r SPCM AQR 14 FC A pair of avalanche photodiodes APDs detect red light emitted by NVs in the diamond sample An APD is similar to an ordinary photodiode in that an incident photon strikes the depletion region of a p n junction creating an electron hole pair The APD is different from a photodiode in the sense that a large reverse bias across the depletion region creates an avalanche effect A single electron liberates many secondary electrons each of which liberate many more secondary electrons and so on Thus a single photon can generate a large electrical signal This is the same process that takes place in photomultiplier tubes but all within a compact solid state device The dark count for the SPCM AQR 14 is less than 100 counts sec Dead time after an event is 50 ns The APD output is a TTL pulse of 2 5 Volts minimum The quantum efficiency is greater than 50 at 650 nm and greater than 35 at 830 nm National Instruments PCIe 6323 X Series Multifunction ePCI card The National Instruments 6323 Data Acquisition card interfaces the computer with the confocal microscope Four analog outputs control both galvo motors the PZT and the microwave attenuator Counter timers count pulses from the APDs synchronize counting with the microwave sweep and count pulses from the SpinCore pulse generator card A rack mounted breakout box National Instruments BNC 2090A incorporates a rear panel connector matching the connectors on the 6323 to front panel BN
41. r a perfect single photon source can be understood as follows When a single photon arrives at a beamsplitter it is either transmitted or reflected resulting in a single photodetector click and vanishing coincidence at 7 Such a behavior of photon photon correlation function represents direct evidence for quantum mechanical nature of light field This is one of the most fundamental phenomena in quantum optics Development of single photon sources is an active field of modern research The NV center has received considerable attention as a robust room temperature source of single photons 2411251126127 and it is currently being used for quantum key distribution and other applications Photon correlation measurements and specifically the width of the anti correlation feature can be used to quantify population dynamics of the NV center Intuitively the counter board measures the probability of photon emission proportional to population of excited state Tle as a function of time triggered by an initial photon emission that prepares the NV center in its ground state Using the rate equation model one finds that ne R R y 1 exp R y t show this where R is optical excitation rate proportional to light intensity and Y is total decay rate from the excited state 81l77 In your experiment you can measure photon correlations for different pump powers and try to use the power dependence to determine the excited st
42. sses through a fast Acousto Optic Modulator AOM rise time 2 5ns allowing pulsed excitation with widths of less than 100 ns and are focused onto the sample with an oil immersion lens Nikon Plan Fluor 100x NA 1 30 To control the position of the focal spot on the sample we employ a closed loop X Y galvanometer combined with a Jaws Magnex held sensor Oi anos Figure 3 Diagram of the experimental setup e 5 SAMPLE ai _ _ _ lt a SILICON PLATE be a gt GLUE Figure 4 Diamond plate is mounted on a silicon wafer It is subjected to a microwave field via a copper wire piezo objective mount for focus adjustment The mirrors forming the galvanometer are imaged onto the back of the objective so that they vary the position of the focal spot without affecting the transmitted laser power Scanning the galvanometer mirrors thus allows us to scan the focal spot over a plane in the sample with a maximum scan range of about 100 x 100 wun Fluorescence from an NV center is collected by the same optical train so that the detection spot is scanned along with the excitation spot The fluorescence into the phonon sideband 650 800nm passes through the dichroic mirrors which combine the excitation lasers with the optical train and a 600 nm long pass filter before being coupled into a single mode fiber In many confocal setups the point source emission is imaged onto a pinhole for backgroun
43. te enclosed optical breadboards house a laser detectors and the confocal microscope respectively See the Detectors photos below These breadboards are in turn mounted on a Thorlabs PTR11104 optical table Accurate optical alignment is critical Consult the faculty or staff before changing the position or angle of any optics Laser The light source is a frequency doubled diode pumped Nd Y AG laser An infrared laser diode pumps a crystal of yttrium aluminum garnet doped with neodymium The neodymium ions emit light at 1064 nm which is frequency doubled in a crystal of potassium dihydrogen phosphate KDP The nominal power of the laser is 200 mW If you open the laser box when the laser is on use the Thorlabs LG 10 laser safety glasses to block both the 532 nm and 1064 nm light The laser power supply is housed in a small black box with a key switch As a safety precaution return the key to the u Ga blue cabinet at the end of each lab session Pa a a Acousto optic modulator Crystal Technology 3080 Confocal microscope block diagram 125 controller 1080A F DIFO 1 0 An acousto optic modulator mounted in the laser box switches the light output off and on The optical element of an AOM is a crystal of tellurium dioxide A piezo electric transducer mounted on the crystal produces an acoustic wave in the crystal in response to an rf voltage across it The light diffracts from the acoustic wave in a process similar to
44. ter sequences for readout Counting Start and Counting 1Length gives the signal count The second counter window defined by parameters Counting2Start and Counting2Length gives the reference count The reference count can be used to normalize the signal count compensating for drifts in alignment green power or other factors that influence the NV fluorescence rate There is no separate initialization green pulse The readout poulse serves to reionize the NV center with 70 efficiency and pump it into m Q Typical parameters for readout are given in the table HARDWARE CHANNELS Bno References 1 1 D Bouwmeester A K Ekert and A Zeilinger Eds The physics of quantum information quantum cryptography quantum teleportation quantum computation Springer Verlag NY 2000 2 J R Maze P L Stanwix J S Hodges S Hong J M Taylor P Cappellaro L Jiang M V Gurudev Dutt E Togan A S Zibrov A Yacoby R L Walsworth and M D Lukin Nanoscale magnetic sensing with an individual electronic spin in diamond http www fas harvard edu phys 19 1r References d4 Maze2008 pdf Nature 455 644 U41 October 2008 3 Lilian Childress Coherent manipulation of single quantum systems in the solid state http www fas harvard edu phys 19 1r References d4 LilyThesis pdf Harvard University 2007 10 11 12 13 14 15 16 17 18 19 20 2i A Len
45. ti bunching Measure Zeeman splitting of the ground and excited states of an n v center Observe Rabi oscillations of a single electron Introduction Control of quantum systems is an important topic in contemporary physics research with many types of experiments aimed at applications ranging from metrology and interferometry to quantum communication and quantum computation The key to realization of these concepts and their potential applications is to gain a control over individual quantum systems such as single photons atoms electrons and nuclei This control should include the ability to prepare and measure such individual degrees of freedom of such systems as well as to manipulate their various degrees of freedom For example secure quantum cryptography can be realized by encoding bits of information into polarization degrees of freedom of individual photons At the same time spin degrees of freedom associated with individual electrons can be used as basic building blocks of quantum information processors quantum bits or as an atomic scale sensors of local fields A A variety of physical systems lend themselves to such investigations and each offers a different set of opportunities and challenges This experiment explores control over individual quantum systems using the so called Nitrogen Vacancy impurity in diamond Such nitrogen vacancy NV centers have been studied for several decades using a variety of spectroscopic
46. turbations the structure of the six electronic excited states remains a topic of current research Vibronic sideband transitions used in excitation are indicated by the yellow continuum b The level diagram corresponding to ground and excited electronic states manifolds including the effect of lattice vibrations The phonon relaxation within each of the manifolds is very fast and the individual vibrational states can not be resolved When the NV center is excited with green light 532 nm it rapidly relaxes to the lowest vibrational state within the excited electronic manifold via phonon emission The spontaneous photon decay of the electronic excited state measured in our experiments can occur directly into the ground state Zero Phonon Line ZPL 637 nm or into excited vibrational states Phonon Side Band PSB from which it relaxes rapidly into the ground state via phonon emission vibronic states are excited using for example a 532 nm laser phonon relaxation brings the NV center quickly into one of the electronic excited states The NV center then fluoresces either via emission of 637 nm ZPL photon or via a process in which photon emission is accompanied by a phonon the so called phonon sideband The fluorescence in phonon sideband PSB is lower in frequency than that of ZPL and extends from 650 800 nm In practice fluorescence into the ZPL accounts for only a few percent of the emitted light 4 thus in the experiment br
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