Research ArticlePHYSICS

Quantum measurement of a rapidly rotating spin qubit in diamond

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Science Advances  04 May 2018:
Vol. 4, no. 5, eaar7691
DOI: 10.1126/sciadv.aar7691
  • Fig. 1 Experimental schematic and setup.

    (A) A diamond containing single NV centers is mounted to the spindle of an electric motor that rotates at 3.33 kHz. Two NV centers located 3 μm below the diamond surface, separated by 3.6 μm, and located 10 μm from the center of the rotation axis (z) are considered in this work. (B) NV centers are optically prepared and addressed by a scanning confocal microscope: 532-nm excitation light is pulsed for a duration tpulse synchronously with the motor rotation, and an avalanche photodiode (APD) collects the emitted photons from the NV center. A time delay tφ between the motor synchronization edge and the optical pulse controls the instantaneous angle of the diamond imaged, and a wire located above the surface of the diamond is used to apply microwave (MW) pulses for state manipulation. Current-carrying coils (not shown) are used to apply magnetic fields along the x, y, and z axes. FPGA, field-programmable gate array.

  • Fig. 2 Strobed confocal microscopy of NV centers.

    (A and B) NV1 and NV2 when stationary (A) and when rotating at high speed (B). Upper panels are x-y plane scans, whereas lower panels are x-z plane scans into the diamond. The color bar describes count rate at the experimental duty cycle of D = 0.67% (peak counts of 1 × 105 recorded for D = 1). The stationary confocal images of NV1 and NV2 are strobed synchronously with an external 3.33-kHz signal from a function generator to yield an equivalent duty cycle to the rotating case. Counts are integrated for 200 ms at each pixel with the laser pulse duration tpulse = 2 μs. (B) The optical illumination and collection are pulsed to be synchronous with the 3.33-kHz rotation of the diamond; blurring resulting from period jitter and wobble of the rotation is evident. NV1 was used for the remainder of the measurements described in this work.

  • Fig. 3 Photoluminescence from a rapidly rotating NV center.

    (A) The NV spin state is determined by collecting fluorescence after the application of a microwave pulse and comparing the photon counts to the same NV when in the mS = 0 bright state. (B) The measured photoluminescence has a truncated Gaussian shape in time due to the motion of the NV through the laser beam. The initial fluorescence from the NV in the mS = −1 dark state is approximately 20 to 30% lower than that after reinitialization into the mS = 0 bright state.

  • Fig. 4 Quantum state control of a rapidly rotating qubit.

    (A) Varying the duration of the microwave pulse in the sequence depicted in Fig. 3A results in time-domain Rabi oscillations, which we detect by computing the normalized fluorescence. a.u., arbitrary units. (B) We demonstrate quantum state control of the NV spin throughout the rotation by first applying a π pulse at t = 0 and then applying a variable duration microwave pulse at t = Trot/2 at which the NV has moved 20 μm away from its initial position. We then observe Rabi oscillations with the NV initialized to the mS = −1 state. Error bars are SE in computed fluorescence ratios from >105 experimental repetitions.

  • Fig. 5 Quantum sensing with a single qubit in a physically rotating frame.

    (A) We examine the phase accumulated over partial rotations by performing a spin-echo experiment for interrogation times τ < 60 μs. Once the final π/2 pulse has projected the NV into the basis state, we wait for the time remaining in the rotation for the NV to return to the preparation/readout region. (B) Unlike the stationary echo signal (gray), we observe nonzero phase accumulation for the rotating NV. The observed fringes originate from the time-varying projection of the magnetic field onto the NV axis due to misalignment from the rotation axis (data points). The observed signal is well described by an 88 ± 29–mG eAC field that is phase-locked to the diamond rotation (fitted line). Error bars are SE in computed fluorescence ratios averaged over three repeated experimental runs of ~106 repetitions.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/5/eaar7691/DC1

    section S1. Stationary spin-echo signal

    section S2. Effect of laser pulse duration

    section S3. Time-dependent optical pumping of the NV

    section S4. Drift during experiments

    fig. S1. Stationary spin-echo signal from NV1.

    fig. S2. Fluorescence smearing due to longer pulse durations.

    fig. S3. Estimation of motor period jitter.

    fig. S4. Dependence of NV contrast on delay time.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Stationary spin-echo signal
    • section S2. Effect of laser pulse duration
    • section S3. Time-dependent optical pumping of the NV
    • section S4. Drift during experiments
    • fig. S1. Stationary spin-echo signal from NV1.
    • fig. S2. Fluorescence smearing due to longer pulse durations.
    • fig. S3. Estimation of motor period jitter.
    • fig. S4. Dependence of NV contrast on delay time.

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