Justin G. Bohnet

National Institute of Standards and Technology, Maryland, United States

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Publications (19)65.88 Total impact

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    ABSTRACT: We theoretically study a superradiant laser, deriving both the steady-state behaviors and small-amplitude responses of the laser's atomic inversion, atomic polarization, and light field amplitude. Our minimum model for a three-level laser includes atomic population accumulating outside of the lasing transition and dynamics of the atomic population distribution causing cavity frequency tuning, as can occur in realistic experimental systems. We show that the population dynamics can act as real-time feedback to stabilize or de-stabilize the laser's output power, and we derive the cavity frequency tuning for a Raman laser. We extend the minimal model to describe a cold-atom Raman laser using $^{87}$Rb, showing that the minimal model qualitatively captures the essential features of the more complex system. This work informs our understanding of the stability of proposed millihertz linewidth lasers based on ultranarrow optical atomic transitions and will guide the design and development of these next-generation optical frequency references.
    11/2013;
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    ABSTRACT: Collective measurements can project a system into an entangled state with enhanced sensitivity for measuring a quantum phase, but measurement back-action has limited previous efforts to only modest improvements. Here we use a collective measurement to produce and directly observe, with no background subtraction, an entangled, spin-squeezed state with phase resolution improved in variance by a factor of 10.5(1.5), or 10.2(6) dB, compared to the initially unentangled ensemble of N = 4.8 x 10^5 87Rb atoms. The measurement uses a cavity-enhanced probe of an optical cycling transition to mitigate back-action associated with state-changing transitions induced by the probe. This work establishes collective measurements as a powerful technique for generating entanglement for precision measurement, with potential impacts in biological sensing, communication, navigation, and tests of fundamental physics.
    10/2013;
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    ABSTRACT: We study the nondemolition mapping of collective quantum coherence onto a cavity light field in a superradiant, cold-atom 87Rb Raman laser. We show theoretically that the fundamental precision of the mapping is near the standard quantum limit on phase estimation for a coherent spin state, Δϕ=1/N, where N is the number of atoms. The associated characteristic measurement time scale τW∝1/N is collectively enhanced. The nondemolition nature of the measurement is characterized by only 0.5 photon recoils deposited per atom due to optical repumping in a time τW. We experimentally realize conditional Ramsey spectroscopy in our superradiant Raman laser, compare the results to the predicted precision, and study the mapping in the presence of decoherence, far from the steady-state conditions previously considered. Finally, we demonstrate a hybrid mode of operation in which the laser is repeatedly toggled between active and passive sensing.
    Physical Review A 07/2013; · 3.04 Impact Factor
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    ABSTRACT: We have realized an atomic sensor that combines active, wideband sensing with passive measurement periods using dynamic control of a cold-atom, superradiant Raman laser. Superradiant lasers have been proposed as highly stable optical frequency references for next generation precision measurement experiments. Collective emission of the atomic gain medium maps the quantum phase of the atomic ensemble onto the detected cavity field. This quantum phase can also be sensitive to the environment, allowing the laser to function as a sensor in addition to a frequency reference. We discuss the fundamental precision of the superradiant mapping and show that the non-demolition measurement can theoretically approach the standard quantum limit on phase estimation for a coherent spin state. Finally, we present experimental demonstrations of a superradiant Raman laser operated as a hybrid active/passive atomic measurement device.
    04/2013;
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    ABSTRACT: We present experimental progress towards quantum non-demolition (QND) measurements of the collective pseudo-spin Jz composed of the maximal mF hyperfine ground states of an ensemble of ˜10^5 ^87Rb atoms confined in a low finesse F = 710 optical cavity. Measuring the phase shift imposed by the atoms on a cavity probe field constitutes a QND measurement that can be used to prepare a conditionally spin squeezed state. By probing on a closed optical transition, we highly suppress both fundamental and technical noise due to Raman scattering compared to probing on an open transition. It may be possible to generate spin squeezed states with >10 dB enhancement in quantum phase estimation relative to the standard quantum limit. The resulting spin squeezed states may specifically enable magnetic field sensing beyond the standard quantum limit as well as broadly impact atomic sensors and tests of fundamental physics.
    04/2013;
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    ABSTRACT: We experimentally study the relaxation oscillations and amplitude stability properties of an optical laser operating deep into the bad-cavity regime using a laser-cooled ^{87}Rb Raman laser. By combining measurements of the laser light field with nondemolition measurements of the atomic populations, we infer the response of the gain medium represented by a collective atomic Bloch vector. The results are qualitatively explained with a simple model. Measurements and theory are extended to include the effect of intermediate repumping states on the closed-loop stability of the oscillator and the role of cavity feedback on stabilizing or enhancing relaxation oscillations. This experimental study of the stability of an optical laser operating deep into the bad-cavity regime will guide future development of superradiant lasers with ultranarrow linewidths.
    Physical Review Letters 12/2012; 109(25):253602. · 7.94 Impact Factor
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    ABSTRACT: Probing the collective spin state of an ensemble of atoms may provide a means to reduce heating via the photon recoil associated with the measurement and provide a robust, scalable route for preparing highly entangled states with spectroscopic sensitivity below the standard quantum limit for coherent spin states. The collective probing relies on obtaining a very large optical depth that can be effectively increased by placing the ensemble within an optical cavity such that the probe light passes many times through the ensemble. Here we provide fundamental expressions for such cavity-aided non-demolition measurements. We also provide experimental examples related to previous work [Phys. Rev. Lett. 106, 133601 (2011)] using quantum non-demolition measurements to prepare conditionally spin-squeezed states in a large ensemble of nearly $10^6$ $^{87}$Rb atoms. Fundamental limits on spectroscopic enhancements in $^{87}$Rb are considered.
    11/2012;
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    ABSTRACT: We demonstrate a proof-of-principle magnetometer that relies on the active oscillation of a cold atom Raman laser to continuously map a field-sensitive atomic phase onto the phase of the radiated light. We demonstrate wideband sensitivity during continuous active oscillation, as well as narrowband sensitivity in passive Ramsey-like mode with translation of the narrowband detection in frequency using spin-echo techniques. The sensor operates with a sensitivity of 190 pT/Hz^(1/2) at 1 kHz and effective sensing volume of 2 * 10^-3 mm^3. Fundamental quantum limits on the magnetic field sensitivity of an ideal detector are also considered.
    Applied Physics Letters 10/2012; 101(26). · 3.79 Impact Factor
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    ABSTRACT: We implement dynamic control of a superradiant, cold atom $^{87}$Rb Raman laser to realize the equivalent of conditional Ramsey spectroscopy for sensing atomic phase shifts. Our method uses the non-demolition mapping of the collective quantum phase of an ensemble of two-level atoms onto the phase of a detected cavity light field. We show that the fundamental precision of the non-demolition measurement can theoretically approach the standard quantum limit on phase estimation for a coherent spin state, the traditional benchmark for Ramsey spectroscopy. Finally, we propose a hybrid optical lattice clock based on this method that combines continuous and discrete measurements to realize both high precision and accuracy.
    08/2012;
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    ABSTRACT: Quantum manipulation protocols for quantum sensors and quantum computation often require many single qubit rotations. However, the impact of phase noise in the field that performs the qubit rotations is often neglected or treated only for special cases. We present a general framework for calculating the impact of phase noise on the state of a qubit, as described by its equivalent Bloch vector. The analysis applies to any Bloch vector orientation, and any rotation axis azimuthal angle for both a single pulse, and pulse sequences. Experimental examples are presented for several special cases. We apply the analysis to commonly used composite $\pi$-pulse sequences: CORPSE, SCROFULOUS, and BB1, used to suppress static amplitude and detuning errors, and also to spin echo sequences. We expect the formalism presented will help guide the development and evaluation of future quantum manipulation protocols.
    Physical Review A 07/2012; 86(3). · 3.04 Impact Factor
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    ABSTRACT: We have realized a cold-atom Raman laser operating deep into the bad-cavity (or superradiant) regime, where the atomic linewidth is much narrower than the cavity linewidth. Here we present our studies on the stability of this active oscillator to external perturbations. We report on the robustness of such an oscillator when implemented in an atomic system with extra degrees of freedom beyond the simple three level model of recent theoretical proposals.
    06/2012;
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    ABSTRACT: We have demonstrated a cold-atom Raman laser operating deep in the bad-cavity (or superradiant) regime, where the atomic linewidth is much narrower than the cavity linewidth. The collective light-atom excitation is stored predominately in the atoms, with intracavity photon number as low as 0.2 photons. The low intracavity photon number isolates the collective atomic dipole from the environment -- a possible future method for overcoming thermal fluctuations of cavity mirrors that presently limit the stability of state-of-the-art lasers. This laser linewidth is measured to be >10^4 below the Schawlow-Townes linewidth that normally applies to good-cavity optical lasers, as well as below single particle linewidths. Our system confirms key predictions that may enable the creation of superradiant lasers using highly forbidden atomic transitions that would have earth-sun coherence lengths, might improve optical atomic clocks by orders of magnitudes, and would contribute to searches for new physics beyond the standard model.
    06/2012;
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    ABSTRACT: The spectral purity of an oscillator is central to many applications, such as detecting gravity waves, defining the second, ground-state cooling and quantum manipulation of nanomechanical objects, and quantum computation. Recent proposals suggest that laser oscillators which use very narrow optical transitions in atoms can be orders of magnitude more spectrally pure than present lasers. Lasers of this high spectral purity are predicted to operate deep in the 'bad-cavity', or superradiant, regime, where the bare atomic linewidth is much less than the cavity linewidth. Here we demonstrate a Raman superradiant laser source in which spontaneous synchronization of more than one million rubidium-87 atomic dipoles is continuously sustained by less than 0.2 photons on average inside the optical cavity. By operating at low intracavity photon number, we demonstrate isolation of the collective atomic dipole from the environment by a factor of more than ten thousand, as characterized by cavity frequency pulling measurements. The emitted light has a frequency linewidth, measured relative to the Raman dressing laser, that is less than that of single-particle decoherence linewidths and more than ten thousand times less than the quantum linewidth limit typically applied to 'good-cavity' optical lasers, for which the cavity linewidth is much less than the atomic linewidth. These results demonstrate several key predictions for future superradiant lasers, which could be used to improve the stability of passive atomic clocks and which may lead to new searches for physics beyond the standard model.
    Nature 04/2012; 484(7392):78-81. · 38.60 Impact Factor
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    ABSTRACT: We describe and characterize a simple, low cost, low phase noise microwave source that operates near 6.800 GHz for agile, coherent manipulation of ensembles of (87)Rb. Low phase noise is achieved by directly multiplying a low phase noise 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency source to provide the desired phase, amplitude, and frequency control. Before modulation, the source has a single sideband phase noise near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting source is estimated to contribute added spin-noise variance 16 dB below the quantum projection noise level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 10(5) (87)Rb atoms.
    The Review of scientific instruments 04/2012; 83(4):044701. · 1.52 Impact Factor
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    ABSTRACT: We report on progress towards a continuous superradiant light source at 795 nm using ˜10^6 ^87Rb atoms trapped in a low finesse (F = 710) optical cavity. Such a light source will probe the physics underlying recent proposals for milliHertz linewidth light sources that would revolutionize the precision of optical clocks and enable long baseline interferometry over earth-to-sun distances. In a superradiant light source, the time phase of a spontaneously generated polarization grating acts as the flywheel for phase information, in place of the intracavity light in a conventional laser. The linewidth of the generated light is predicted to fall well below both the Schawlow-Townes limit for conventional lasers and the single particle decoherence rate. Importantly, the frequency of the emitted light is predicted to be highly insensitive to the thermal mirror motion that currently limits the narrowest of lasers.
    06/2011;
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    ABSTRACT: We use the vacuum Rabi splitting to perform quantum nondemolition measurements that prepare a conditionally spin squeezed state of a collective atomic psuedospin. We infer a 3.4(6) dB improvement in quantum phase estimation relative to the standard quantum limit for a coherent spin state composed of uncorrelated atoms. The measured collective spin is composed of the two-level clock states of nearly 10(6) (87)Rb atoms confined inside a low finesse F=710 optical cavity. This technique may improve atomic sensor precision and/or bandwidth, and may lead to more precise tests of fundamental physics.
    Physical Review Letters 04/2011; 106(13):133601. · 7.94 Impact Factor
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    ABSTRACT: We demonstrate that the collective vacuum Rabi splitting can be used to perform quantum nondemolition measurements on the clock states of 10^6 ^87Rb atoms in an optical cavity. We observe a 13(1) dB increase in sensitivity over sampled measurements and a precision 8.6(2.6) dB below the projection noise level. We infer the preparation of spin squeezed states with sensitivities 3.4(6) dB below the standard quantum limit and directly observe a 1.1(4) dB spectroscopic improvement. The measurement is enhanced using a large ensemble and may lead to more precise atomic sensors.
    10/2010;
  • Zilong Chen, Justin G. Bohnet, Dai, James K. Thompson
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    ABSTRACT: We demonstrate QND measurements on an ensemble of 10^6 ^87Rb atoms. Quantum state-dependent populations are determined at the projection noise level by measurements of the collective Vacuum Rabi Splitting for the resonantly coupled atom-cavity system. The splitting is measured by simultaneously scanning the frequency of two probes across the two transmission resonances and phase coherently detecting the full IQ response of the reflected electric fields. Measurement back-action imposes AC Stark shifts on the atoms, resulting in a reduction of the Ramsey fringe contrast due to inhomogeneity in the probe-atom coupling. We show that the spin-echo sequences that will be needed to achieve atomic spin-squeezing on the Rb clock transition also strongly suppress these AC stark shifts. The remaining probe-induced decoherence is close to the fundamental limit imposed by free space scattering of the probe photons.
    03/2010;
  • Zilong Chen, Dai, Justin G. Bohnet, James K. Thompson
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    ABSTRACT: Current state-of-the-art microwave atomic clocks are limited by quantum projection noise associated with uncorrelated atoms. The current generation of neutral atom optical atomic clocks have already reached a frequency stability very close to the projection noise limit. By using entangled atoms, precision better than the projection noise limit can be obtained, so generating significant amounts of squeezing is of practical interest to the current generation of atomic clocks and precision measurement experiments. We will report experimental progress on generating spin squeezing via optical resonator-enhanced, collective Quantum Non-Demolition measurements on large ensembles of Rubidium 87 atoms.
    01/2009;

Publication Stats

11 Citations
444 Views
65.88 Total Impact Points

Institutions

  • 2012
    • National Institute of Standards and Technology
      Maryland, United States
  • 2011–2012
    • University of Colorado at Boulder
      • Department of Physics
      Boulder, CO, United States
    • University of Colorado
      • Department of Physics
      Denver, Colorado, United States