Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session T7: Quantum Measurement |
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Chair: Alberto Marino Valle, University of Oklahoma Room: 313 |
Friday, June 9, 2017 8:00AM - 8:12AM |
T7.00001: Continuous monitoring of a quantum state beyond classical limits Giorgio Colangelo, Ferran Martin Ciurana, Robert J Sewell, Morgan W Mitchell Continuous monitoring of a quantum system is essential to high-sensitivity measurement of time-varying quantities. Precession of a spin ensemble may be monitored by measuring spin projectors $F_\alpha$ at different times. Since these projectors do not commute, quantum measurement back-action (QMBA) necessarily enters the measurement record, introducing errors and limiting sensitivity. Here we show how to reduce this disturbance below $\delta F_\alpha \sim \sqrt{ N}$, the classical limit for $ N$ spins, by directing the QMBA almost entirely into an unmeasured spin component. This generates a {\bf planar squeezed state} which allows simultaneous precise knowledge of spin angle and amplitude. We demonstrate continuous monitoring of a precessing spin ensemble with steady-state angular sensitivity 2.9~dB beyond the standard quantum limit, simultaneous with amplitude sensitivity 7.0~dB beyond Poisson statistics, surpassing classical limits in non-commuting observables for the first time. Our method is close to practical application in high-performance atomic sensors, such as magnetometers and clocks, and is compatible with multi-pass and cavity build-up methods. [Preview Abstract] |
Friday, June 9, 2017 8:12AM - 8:24AM |
T7.00002: Order of Magnitude Improvement in NV Ensemble T2* via Control and Cancellation of Spin Bath Induced Dephasing Connor Hart, Erik Bauch, Jennifer Schloss, Matthew Turner, John Barry, Ronald Walsworth We deploy two complementary techniques, spin bath control and double quantum magnetometry, to attain up to a 14-fold improvement in $T_2^*$ for Nitrogen-Vacancy ensembles in diamond. Depending on the Nitrogen concentration of the sample, three regimes can be differentiated: for low concentrations ($N \ll 1$ ppm), the dephasing is strain-dominated and can be suppressed by working in the NV's double quantum basis $\{-1, +1\}$. In an intermediate regime ($N \simeq 1$ ppm), the combination of double quantum and spin bath control achieves a 14-fold increase in $T_2^*$. At greater Nitrogen concentrations ($N \geq 10$ ppm), dipolar interactions with electronic Nitrogen spins dominate the broadening which are mitigated by spin bath driving. Our results elucidate sources of dephasing over a range of spin concentrations and outline a direct path forward to improving coherence times for sensing and quantum science. [Preview Abstract] |
Friday, June 9, 2017 8:24AM - 8:36AM |
T7.00003: Reaching the Quantum Cram\'{e}r-Rao Bound for Transmission Measurements Timothy Woodworth, Kam Wai Clifford Chan, Alberto Marino The quantum Cram\'{e}r-Rao bound (QCRB) is commonly used to quantify the lower bound for the uncertainty in the estimation of a given parameter. Here, we calculate the QCRB for transmission measurements of an optical system probed by a beam of light. Estimating the transmission of an optical element is important as it is required for the calibration of optimal states for interferometers, characterization of high efficiency photodetectors, or as part of other measurements, such as those in plasmonic sensors or in ellipsometry. We use a beam splitter model for the losses introduced by the optical system to calculate the QCRB for different input states. We compare the bound for a coherent state, a two-mode squeezed-state (TMSS), a single-mode squeezed-state (SMSS), and a Fock state and show that it is possible to obtain an ultimate lower bound, regardless of the state used to probe the system. We prove that the Fock state gives the lowest possible uncertainty in estimating the transmission for any state and demonstrate that the TMSS and SMSS approach this ultimate bound for large levels of squeezing. Finally, we show that a simple measurement strategy for the TMSS, namely an intensity difference measurement, is able to saturate the QCRB. [Preview Abstract] |
Friday, June 9, 2017 8:36AM - 8:48AM |
T7.00004: A sensitive electrometer based on a Rydberg atom in a SchrÃ¶dinger-cat state Sebastien Gleyzes, Adrien Facon, Eva-Katharina Dietsche, Arthur Larrouy, Dorian Grosso, Serge Haroche, Jean-Michel Raimond, Michel Brune Metrology experiments based on the measurement of small rotation of a large angular momentum are limited by the projection noise. When the measurement is performed using classical states, the precision cannot exceed the standard quantum limit (SQL), that scales like $1/\sqrt J$. To beat the SQL, one needs to make use of non-classical states. Our system is a Rydberg atom with a large quantum principal number $n \sim 50$. In the presence of a small electric field, the degeneracy between levels with the same n is lifted. Then, using a radio frequency field with a well-defined polarization, it is possible to restrict the evolution of the atom to a subspace of the Rydberg manifold where the system behaves like a large spin $J = (n-1)/2$, whose frequency is proportional to the local amplitude of the electric field. We have used this effective spin to perform a quantum-enabled measurement of the static electric field [1]. We prepare a SchrÃ¶dinger cat state of the Rydberg atom, and observe how the quantum phase of the cat provides a very sensitive signal to measure the variation of the static electric field allowing us to go beyond the SQL. \\$[1]$ A. Facon, \textit{et al}, Nature \textbf{535}, 262-265 (2016) [Preview Abstract] |
Friday, June 9, 2017 8:48AM - 9:00AM |
T7.00005: Spin-motion coupling for sensitive amplitude detection with large ion crystals Justin G. Bohnet, Kevin A. Gilmore, Brian C. Sawyer, Joseph W. Britton, John J. Bollinger During the past decade, optomechanical systems have shown increasingly sensitive techniques for measuring a mechanical oscillator's amplitude, using the coupling of the oscillator to an optical field. Here we present experimental measurements of the amplitude of a center-of-mass (COM) drumhead motion of a 2D ion crystal composed of 100 ions in a Penning trap using a spin-dependent, optical-dipole force to couple the oscillator to the electron spin of the trapped ions. For motion off-resonant with the trap axial frequency we demonstrate measurements of amplitudes as small as 50 pm, 40 times below the ground state zero-point fluctuations. We show the sensitivity of our technique is limited by the quantum projection noise of the trapped ions. In the future, we expect to achieve a sensitivity of (20 pm)/$\sqrt{\mathrm{Hz}}$, which can be useful for detecting extremely weak forces ($<1$ yN) and electric fields, as well as exploring protocols for sensing beyond the standard quantum limit for force detection. [Preview Abstract] |
Friday, June 9, 2017 9:00AM - 9:12AM |
T7.00006: The role of thermal motion in free-space light-atom interaction Yue Sum Chin, Matthias Steiner, Christian Kurtsiefer \noindent The prospects of distributed quantum networks have triggered much interest in developing light-matter interfaces. While this is usually realized by optical resonators, tightly focused free-space interfaces offer a complementary alternative. Our version of free-space light-matter interface is formed by a pair of high numerical aperture (NA=0.75) lenses and a single atom held in an optical tweezer. Operating near the diffraction limit, we demonstrate 17.7\% extinction of a weak coherent field by a single atom. The thermal motion of the atom is commonly suspected to be one of the limiting factors of the interaction. Here we verify quantitatively this effect by measuring in-situ the interaction strength as the atom heats up. \\ \\ \noindent[1] Y.S. Chin, M. Steiner, C. Kurtsiefer, arxiv.org, arXiv:1611.08048 (2016). [Preview Abstract] |
Friday, June 9, 2017 9:12AM - 9:24AM |
T7.00007: Quantum Sensing Beyond the Shot-Noise Limit with Plasmonic Sensors Mohammadjavad Dowran, Ashok Kumar, Benjamin Lawrie, Raphael Pooser, Alberto Marino The use of quantum resources offers the possibility of enhancing the sensitivity of a device beyond the shot noise limit and promises to revolutionize the field of metrology through the development of quantum enhanced sensors. In particular, plasmonic sensors, which are widely used in bio-chemical sensing applications, provide a unique opportunity to bring such an enhancement to real-life devices. Resonance plasmonic sensors respond to changes in refractive index through a shift of their characteristic transmission spectrum. We show that the use of quantum squeezed states to probe plasmonic sensors can enhance their sensitivity by lowering the noise floor and allowing the detection of smaller changes in refractive index. In our experiment, we use one of the beams of a two-mode squeezed state generated via four-wave-mixing in Rb atoms to probe the sensor. A squeezing level of 4~dB is obtained after transduction through the plasmonic sensor, which consists of a triangular nano-hole array in a thin silver film and exhibits a sensitivity of the order of $10^{-10}$~RIU$/\sqrt{\rm{Hz}}$. The use of quantum states leads to $40\%$ enhancement in the sensitivity of the plasmonic sensor with respect to the shot noise limit. [Preview Abstract] |
Friday, June 9, 2017 9:24AM - 9:36AM |
T7.00008: Generation of atomic spin squeezed states in nanophotonic waveguides using QND measurement Xiaodong Qi, Jongmin Lee, Yuan-Yu Jau, Ivan Deutsch Nanophotonic waveguides strongly enhance the entangling strength of the atom-light interface. We study their application to the generation of spin squeezed states of trapped ultracold cesium atoms in two geometries --- cylindrical optical nanofibers and square waveguides. We consider two different protocols --- squeezing the clock transition by the birefringence coupling and squeezing a spin coherent state via the Faraday interaction. We unify our analysis based on a universal parameter --- the optical depth per atom. In calculating the spin squeezing parameter, we have established a set of stochastic master equations to describe the individual and collective spin dynamics. Our simulation shows that \textasciitilde 10 dB of spin squeezing may be achievable with a few thousands of atoms on these nanophotonic waveguides. Our result can be generalized to other nanophotonic platforms, for implementing non-Gaussian states, and to improve quantum sensing precision using spin squeezing techniques. [Preview Abstract] |
Friday, June 9, 2017 9:36AM - 9:48AM |
T7.00009: Measuring signatures of quantum chaos in strongly-interacting systems Gregory Bentsen, Brian Swingle, Monika Schleier-Smith, Patrick Hayden Strongly-coupled many-body quantum systems generically exhibit signatures of quantum chaos. Recent theoretical work on black holes has focused on probing these signatures using so-called ``out-of-time-order" (OTO) correlation functions, which measure a quantum-mechanical version of the classical butterfly effect. We propose a general echo-type protocol to experimentally measure these correlators in arbitrary many-body systems that involves reversing the sign of the Hamiltonian [1]. We detail a realistic implementation in a single-body system employing cold atoms and cavity quantum electrodynamics to verify feasibility with current technology. Applying this protocol to diverse experimental systems could place bounds on quantum information processing, uncover new bounds on transport coefficients, offer insight into closed-system thermalization, and perhaps even enable experimental tests of the holographic principle.\\ [1] B. Swingle, G. Bentsen, M. Schleier-Smith, P. Hayden, Phys. Rev. A 94, 040302(R) (2016) [Preview Abstract] |
Friday, June 9, 2017 9:48AM - 10:00AM |
T7.00010: Distinguishing time-reversible from time-irreversible processes with Interference patterns. Zilin Chen, Peter Beierle, Herman Batelaan In interference experiments, coherence is often incomplete. Coherence can be lost by dephasing or decoherence processes. The former is associated with time-reversible processes, while the latter is associated with time-irreversible processes. Even though there is a significant difference, the interference patterns appear similar; the pattern are more or less washed out. Entropy is a convenient measure of time reversibility. However, to determine the entropy, the coherence terms, i.e., the off-diagonal elements of the density matrix, need to be known. At first glance, it seems not possible to determine the reversibility from an interference pattern that provides only knowledge of the diagonal elements of the density matrix. Inspired by the lens-less imaging experiments by Gao et al.[1], we show by theoretical analysis that the spatial correlation function of repeated measurements of the interference pattern allows one to assess the reversibility. The second-order correlation function is proportional to the Fourier transformation of the spatial pattern of the double slits, but only if a dephasing process disturbs the wave. For a decoherence process the interference pattern is not recovered. This provides a method to establish time-reversibility, or the absence thereof, in matter-wave experiments. [1] Rui-Feng L, Xin-Xing Y, Yi-Zhen F, et al. Subwavelength Fourier-transform imaging without a lens or a beamsplitter[J]. Chinese Physics B, 2014, 23(5): 054202. [Preview Abstract] |
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