Frequency Tunable Atomic Magnetometer based on an Atom Interferometer

Transcription

1 Frequency Tunable Atomic Magnetometer based on an Atom Interferometer D.A. Braje 1, J.P. Davis 2, C.L. Adler 2,3, and F.A. Narducci 2 Blaubeuren Quantum Optics Summer School 29 July MIT Lincoln Laboratory, Lexington, MA 2 Naval Air Systems Command, Patuxent River, MD 3 St. Mary s College of Maryland, Saint Mary s City, MD Also thanks to S. A. DeSavage, R. Forster and Z. Switzer $$$$$$$$$$ ONR NavAir CTO $$$$$$$$$$ The Lincoln Laboratory portion of this work is sponsored by the Assistant Secretary of Defense for Research & Engineering under Air Force Contract #FA C Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the United States Government.

2 Outline Magnetometry / Gradiometry Motivation Applications: Remote Sensing, Security, Biomagnetics, Navigation Gradiometry Atom Interferometer Magnetometer Atom Interferometer Concept NMR Pulse Sequences for Atoms Experimental Results Clock Transition Ramsey vs. Hahn Echo This is data

3 Airborne Magnetic Noise MAD ELF 10 Geology 0.5 Spectral Density (nt/hz ) CPA=1000 ft CPA=2000 ft 8 3 3x10 nt-ft Dipole Buffeting Swell Platform Maneuver P-2000 Geomagnetic ASQ ELF Frequency (Hz) NIST Welch Budker Romalis ~ ft/hz 1/2

4 Motivation: (classical) gradiometer example P2000 Gradiometer Test Memorial Airfield, Chandler AZ April B Noise Noise Field [nt] 0 B-Field B Object -0.8 Even an Admiral can see this! Time [hrs] 1 2 Car Distance Field [nt] ft 1 2 P2000 Sensors 80 ft Sensitivity: 500 pt/(80ft) Time [hrs] AI Gradiometer Sensitivity: 0.2 pt/m

5 Atom Interferometry Applications Clocks Frequency standards Navigation, communication, synchronization Magnetometers Magnetic anomaly detection (i.e. submarines, unexploded ordinance, mines), detection of dangerous liquids and uranium, biomagnetics, navigation Accelerometers, Gyroscopes Arrayed for differential acceleration, gravimeters, etc Navigation, seismology, mass anomaly detection (minerals, bunkers, natural resources) Fundamental laws of physics Navigation Detection / Security Biomagnetics Language is common to the worlds of NMR and quantum computing

6 Keep Sensitivity; Design Around the Noise Cannot remove magnetic noise in remote sensing 1. Filter out of band noise 2. Measure magnetic field gradient (Gradients used for object location) B-Field nt pt ft Rev. Sci. Instrum. 77, (2006) Commercially-available SQUIDS mhz Frequency Hz khz Shielded Room

7 Outline Magnetometry / Gradiometry Motivation Applications: Remote Sensing, Security, Biomagnetics, Navigation Gradiometry Atom Interferometer Magnetometer Atom Interferometer Concept NMR Pulse Sequences for Atoms Experimental Results Clock Transition Ramsey vs. Hahn Echo This is data

8 Two level atom reminder Powerbroadened Linewidth Natural Linewidth

9 Raman Resonances Now controlled by ground state decoherence time which can be made very small

10 φ = µ B + ( k1 k 2 ) ( g F ' m F ' gt 2 g F m F ) T / 2 0 B( t) t T T / 2 3 Atom Interferometer: B( t) t x Time Domain Davis & Narducci, JMO (2008) Zhou et al. PRA (2010) π/2 π π/2 1 2 g ν HF ω 2 ω Co-propagating Raman beams: Doppler-free T t Pseudospin Representation: 1 π/2 1 π π/2 1 y 2 2 2

11 Magnetic Gradient (spin echo) Interferometer not quite

12 Ramsey (π/2 π/2)

13 Spin Echo (π/2 π π/2)

14 (Unbalanced) Spin echo (π/2 π π/2)

15 Atom Interferometer: Frequency Domain x π/2 π π π π π π/2 Pulse sequence controls interferometer sensitivity to noise π/2 1 π π/2 T t Scanning number of pulses can map out magnetic noise spectral density g(ω) μ φ = ) N = 10 B( t δt T 2T B ( g F ' mf ' g FmF B( t) δt ) 0 T µ φ = Frequency [khz] B ( g F ' mf ' g FmF ) B T

16 Filter Functions Frequency Domain N = 0 N = 1 T = 1 ms T = 1000 us T = 500 us N = 1 Hahn Echo N = 5 N = 10 T = 250 us N pulses π/2 π π π π/2 π/2 π π/2 T = 1 ms T/2 T/2

17 State preparation well defined qubit initialization Unshielded environment and in a metal canister! Gradient coils 10 G/cm Trapping lasers: Amplified (TA7613) New Focus StableWave cm beam F' = P 3/2 Trapping F' = 3 F' = 2 F' = 1 Repump F = S 1/2 F = 2

18 Apparatus Trapping Setup Raman Lasers

19 Experimental schematic Trapping Beam 0 +1 Beat note MOT Sat Abs ECDL HWP AMP AO1 +1

20 Timing sequence Trapping B-Field 85 Rb ~10 7 atoms; ~300 µk; F = 2 Repump Field Trapping Field EXPERIMENT Readout Time [ms] Well-defined coherent qubit Initialize Gate operations Readout F' = 4 F' = 4 F' = 4 F' = P 3/2 F' = 3 F' = 2 F' = P 3/2 F' = 3 F' = 2 F' = P 3/2 F' = 3 F' = 2 F' = P 3/2 Trapping Repump Trapping Readout Raman F' = 3 F' = 2 F' = 1 F = 3 F = 3 F = 3 F = S 1/2 5 2 S 1/2 5 2 S 1/2 5 2 S 1/2 F = 2 F = 2 F = 2 F = 2

21 A real atom: 85 Rb 11 different Raman resonances!

22 Raman spectra (arbitrary field) F' = 4 11 different Raman resonances 5 2 P 3/2 F' = 3 F' = 2 F' = 1 p3 υ = 1 T pulse F = S 1/2 F = 2 Two photon detuning [khz] 85 Rb ~10 7 atoms ~300 µk F = 2

23 Use to zero field around atoms Optical Spacing Current (amps) Field 1 Field 2 Optical Spacing Current (amps) Optical Spacing Current (amps) 25 Field 3

24 Single Peak 26

25 Selection Rules

26 Six Peaked Spectrum PQE 03 Jan 2011 Transverse

27 Five Peaked Spectrum PQE 03 Jan 2011 Longitudinal

28 Effect of pulse shape

29 Square vs Gaussian Pulses Square Pulse Gaussian Pulse 31

30 Hybrid Pulse

31 Crude Magnetometer PQE 03 Jan min of 0.25Hz Now can do up to 10 Hz 33

32 Rabi cycling: m=0 to m'=0 transition universal gates ability to read out F' = P 3/2 F' = 3 F' = 2 F' = 1 T Raman Readout F = 3 Time 5 2 S 1/2 R - AOM F = 2 π υ = 1 T pulse ν HF /2 R + π/2 Two photon detuning T Raman [ms]

33 Ramsey interference

34 Ramsey vs. double delay T=10 µsec T=30 µsec As time between pulses is lengthened, Ramsey interference disappears. Increasing T T=50 µsec T=70 µsec

35 Atom Interferometer Clock Transition T m = -1 m = 0 m = +1 Two-Photon Detuning [khz] 3 ω 2 ω 1 ν HF 2 1

36 Atom Interferometer Magnetometer

37 Atom Interferometer Magnetometer Ramsey (Magnetic) Spin Echo (Magnetic) T 2 * ~ 55 us T 2 e ~ 55 us π/2 π/2 π/2 π π/2

38 Conclusions Magnetometry is useful for a broad range of applications from biomagnetics to remote detection Atom Interferometry allows NMR like pulse control sequences as a lock-in-amplifier for magnetic signals Using these techniques combined with gradiometry, we can detect signals in a magnetically noisy environment

39 Thank you for your attention! Questions?

40 Other experiments-then could be interesting. But it s not fundamental enough maybe Photo courtesy J. Mandel Leonard Mandel

41 Bonus Material

42 Multiple Pulse Interferometer Sequences π/2 π π/2 g(ω) N = 1 T/2 T/2 Frequency [khz] π/2 π π π π/2 g(ω) N = 3 Frequency [khz] NMR: Carr Purcell PR (1954) Ions: Biercuk Nature (2009) Atoms: Davidson PRL 105, (2010) NV Centers: Lukin, Rugar, Cappellaro Superconductors: Bylander Nature Phys (2011)

43 F' = 4 Rabi cycling: m 0 to m transition 0 universal gates ability to read out 5 2 P 3/2 F' = 3 F' = 2 F' = 1 T Raman Readout F = 3 Time 5 2 S 1/2 R - AOM F = 2 π υ = 1 T pulse ν HF /2 R + π/2 T Raman [ms] Two photon detuning

44 φ = µ B + ( k1 k 2 ) ( g F ' m F ' gt 2 g F m F ) T / 2 0 B( t) t T T / 2 Atom Interferometer B( t) t x ω 2 π/2 π π/2 3 1 g Davis & Narducci, JMO (2008) Zhou et al. PRA (2010) 2 ω 1 ω 2 ω 1 ν HF T/2 T t 2 π/2 2 π π/2 2 y 1 1 1

45 Magnetically sensitive Ramsey interferometer π/2 π/2 T (Double Delay) Double Delay [us] g(ω) g(ω,τ) = sinc 2 [ωτ /2] Frequency [khz] Two-photon Detuning [khz]

46 Atom Interferometer Magnetometer Rabi flopping in a magnetically noisy environment:

47 Sensitivity

48 Filter Functions Time / Frequency Domain

49 Keep Sensitivity; Design Around the Noise Cannot remove magnetic noise in remote sensing 1. Filter out of band noise 2. Measure magnetic field gradient (Gradients used for object location) B-Field nt pt ft Rev. Sci. Instrum. 77, (2006) Commercially-available SQUIDS mhz Frequency Hz khz Shielded Room

50 Homecoming Lorenzo Narducci Leonard Mandel Photo courtesy J. Mandel

51 17 years later

52 Other experiments-then could be interesting. But it s not fundamental enough Photo courtesy J. Mandel Leonard Mandel

53 Definition of π pulse π

54 Definition of π/2 pulse π/2