Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E32: Quantum Metrology and Sensing IVLive

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Sponsoring Units: DQI Chair: Mihika Prabhu, Massachusetts Institute of Technology MIT 
Tuesday, March 16, 2021 8:00AM  8:12AM 
E32.00001: NearDeterministic Collective nonLinear WeakValue Metrology Muthumanimaran Vetrivelan, Sai Vinjanampathy Weakvalue amplification (WVA) involve postselection measurements on an evolved state and using the measurements to enhance a parameter of interest. Since postselection involves rejecting all the undesirable outcomes, there exists a tradeoff between the postselection probability of the desired measurement and the amplification produced by the apparatus. This tradeoff has always limited the applicability of weakvalue metrology. This issue was partially resolved by Pang and Brun who proposed that collective effects can enhance WVA. A full solution where a simultaneous superextensive enhancement in both the success probability and the weak value amplification is still lacking. we resolve this completely by considering nonlinear collective Hamiltonians and demonstrate that they enhance existing WVA schemes. We demonstrate a linear enhancement in the weakvalue and a simultaneous quadratic enhancement in the success probability 
Tuesday, March 16, 2021 8:12AM  8:24AM Live 
E32.00002: Bipartite energytime uncertainty relation and quantum error correction for metrology with noise Philippe Faist, Mischa Woods, Victor Albert, Joseph M Renes, Jens Eisert, John P Preskill Noise in quantum metrology reduces the sensitivity to which one can determine an unknown parameter in the evolution of a quantum state, such as time. Here, we consider a noiseless quantum system (a probe, or a clock) prepared in a pure state that encodes some time t, on which we apply an arbitrary noise channel. We show an uncertainty relation stating that the noisy probe’s sensitivity to time trades off exactly with the environment’s sensitivity to the energy of the noiseless probe. We obtain necessary and sufficient conditions for when zero sensitivity is lost after application of the noise channel. These conditions are analogous to the KnillLaflamme quantum error correction conditions but they are easier to satisfy. I will discuss applications to manybody quantum metrology with strongly interacting particles, where we construct probe states that satisfy our condition and are therefore robust against local noise. For a 1D spin chain with nearestneighbor interactions subject to amplitude damping noise on each site, we verify numerically that our probe state does not lose any sensitivity to first order in the noise parameter. 
Tuesday, March 16, 2021 8:24AM  8:36AM Live 
E32.00003: Quantum limit of superresolution with a noisy imaging system Changhun Oh, Sisi Zhou, Yat Wong, Liang Jiang Rayleigh criterion for resolving two incoherent point sources is most widely used for assessing the resolution of an imaging system. After a remarkable proposal of a scheme to beat the Rayleigh limit using a structured coherent measurement [1], the superresolution technique has been paid attention to both theoretically and experimentally, while studies for the effect of noise on superresolution are limited yet. Here, we demonstrate the impact of noise, such as thermal noise and dark counts, on the superresolution scheme to resolve two identical point sources of an arbitrary state and show by using Fisher information that the ultimate resolution drops rapidly in the presence of noise [2]. As an example, we provide an analysis of the effect of noise on resolving two thermal objects. Finally, we show that a spatial mode multiplexing method is nearly optimal to resolve two thermal point sources in the presence of noise. 
Tuesday, March 16, 2021 8:36AM  8:48AM Not Participating 
E32.00004: Fundamental limits of Spectroscopy with Quantum Light Evangelia Bisketzi, Animesh Datta Spectroscopy with quantum light is a newly emerging field in which the quantum nature of 
Tuesday, March 16, 2021 8:48AM  9:00AM 
E32.00005: Optimal Measurement of Field Properties with Quantum Sensor Networks Timothy Qian, Jacob Bringewatt, Igor Boettcher, Przemyslaw Bienias, Alexey V Gorshkov We consider a quantum sensor network of qubit sensors coupled to a field f(x;θ) analytically parameterized by the vector of parameters θ. The qubit sensors are fixed at positions x_{1}...x_{d}. While the functional form of f(x;θ) is known, the parameters θ are not. We derive saturable bounds on the precision of measuring an arbitrary analytic function q(θ) of these parameters and construct the optimal protocols that achieve these bounds. Our results are obtained from a combination of techniques from quantum information theory and duality theorems for linear programming. They can be applied to many problems, including optimal placement of quantum sensors, field interpolation, and the measurement of functionals of parametrized fields. 
Tuesday, March 16, 2021 9:00AM  9:12AM Live 
E32.00006: Quantum enhanced telescopes beyond the Gottesman protocol Robert Czupryniak, John Steinmetz, Paul G Kwiat, Andrew N Jordan Interferometric techniques have been studied intensively in astronomy since they offer a significant improvement in angular resolution over the direct detection methods. We analyze the entanglementassisted longbaseline interferometric procedures and investigate potential improvements. Gottesman et al. [1] has shown that one can use the concepts known in quantum information theory in longbaseline interferometry to examine stellar objects given that they are weak thermal sources. Khabiboulline et al. [2] proposed another method based on networks of quantum memories. Here we propose an entanglementassisted interferometric procedure that can extract more information about the stellar source from each photon it emits when compared to the procedure given in [1]. We also investigate the methods without the burden of the quantum memory implementation requirement. 
Tuesday, March 16, 2021 9:12AM  9:24AM Live 
E32.00007: Windchime: first steps towards realizing mechanical detector arrays for particle physics Sohitri Ghosh Recent advances in the mechanical sensing technologies provide a novel pathway in searches for dark matter and other particle physics targets. The operations of individual sensors are now approaching the quantumlimited regime, where the sensitivity is set by noise caused by Heisenberg uncertainty. However, the scalability of these devices to large arrays remains a key challenge to be addressed before the full benefit of these sensors can be realized, including improved sensitivity, energy and direction estimation, and background rejection. Here we discuss the initial progress made by the Windchime collaboration, an interdisciplinary group of quantum sensing and particle physics researchers, in the construction and operation of an array of many mechanical sensors to search for dark matter. Such an array will have immediate reach for novel searches for certain ultralight and composite dark matter particles, and ultimately could be used for direct detection purely through gravity. 
Tuesday, March 16, 2021 9:24AM  9:36AM Live 
E32.00008: Neutron Optics Theory for Entangled Neutron Beams Shufan Lu, Kylie A Dickerson, William Michael Snow The theory of singleparticle entangled neutron scattering from entangled degrees of freedom in condensed matter is under development [1]. By the optical theorem of scattering theory, entanglementdependent effects in nonforward scattering must also appear at some level in the forward direction, which is the domain of neutron optics. We will discuss the steps we have taken toward this development [2,3] and present applications in neutronantineutron oscillations under mirror reflection conditions [4]. 
Tuesday, March 16, 2021 9:36AM  9:48AM Live 
E32.00009: Advantages of ModeEntangled Neutrons in QuantumEnhanced Measurements Samuel McKay, David Verge Baxter, Collin Leslie Broholm, Abu Ashik Md. Irfan, Stephen Kuhn, Gerardo Ortiz, Roger Pynn, Jiazhou Shen, William Michael Snow, Vincent Vangelista We present multimode entanglement of individual neutrons and suggest that beams of such neutrons may constitute a new quantum probe of materials. We have experimentally generated bipartite (spinpath) and tripartite (spinpathenergy) modeentangled neutron beams using neutron interferometers configured for a short separation between paths (between 85 nm and 1600 nm). The entanglement is proven by the violation of contextuality inequalities, similar to the Bell inequality. We discuss the distinguishability condition of the paths, which we show is robust even when the separation is less than the neutron’s transverse intrinsic coherence length. The entanglement was demonstrated in a variety of beamline configurations, with the transverse beam coherence length ranging from 75 nm to 600 nm. We speculate that such beams could prove useful for increased precision in searches for exotic couplings (e.g. spingravity etc.) at length scales that have previously been unavailable, particularly if additional degrees of freedom can be added to the entanglement, such as orbital angular momentum states. 
Tuesday, March 16, 2021 9:48AM  10:00AM Live 
E32.00010: Qubit Quantum Metrology in the Regime of Limited Resources Jason Saunders, JeanFrancois S Van Huele It has been demonstrated that quantum resources, such as entanglement, can decrease the uncertainty of parameter estimation. A tight lower bound for this uncertainty exists for the regime of asymptotic measurement resources. Several bounds have been proposed for the more realistic nonasymptotic regime, but none are tight. We investigate the regime of nonasymptotic resources for a specific system: using nu qubit probes to estimate a rotation angle externally induced on the probes. We introduce a Bayesian modeling framework for qubit quantum metrology. We numerically investigate the effect of quantum correlations on parameter estimation uncertainty as a function of nu. We find that, even in the nonasymptotic regime, increased entanglement results in a lower uncertainty. However, the uncertainty measured by probes with intermediate amounts of entanglement exhibits more variation than either separable probes or maximally entangled probes. 
Tuesday, March 16, 2021 10:00AM  10:12AM Live 
E32.00011: Tight bounds on the simultaneous estimation of incompatible parameters Jasminder Sidhu, Yingkai Ouyang, Earl Campbell, Pieter Kok Quantum sensors are in the vanguard of new quantum technologies. The theoretical foundation of these sensors is quantum estimation theory, which provides fundamental bounds to the precision with which we can measure physical signals. A widely used limit is the quantum CramérRao bound (QCRB). 
Tuesday, March 16, 2021 10:12AM  10:24AM Live 
E32.00012: A Multiconfigurational Study of Negatively Charged NitrogenVacancy Center in Diamond Churna B Bhandari, Aleksander Wysocki, Sophia Economou, Pratibha Dev, Kyungwha Park Point defects in wide bandgap semiconductors have been shown to be promising for quantum sensing and information applications. Discoveries of new point defects tailored for specific applications require quantitatively reliable predictions of electronic and magnetic properties of pointe defects. Manyelectron characteristics of the defect states demand theories beyond singleelectron approach. Taking advantage of the spatially localized nature of the defects, we apply multiconfigurational quantumchemistry methods to a prototype point defect such as a negatively charged nitrogenvacancy center in diamond. Our methodology takes into account electron correlation, spinorbit coupling (SOC) and dipolar spinspin coupling (SSC) within manyelectron configurations without fitting parameters. We find the correct ordering of the singlet and triplet states and identify the manyelectron configurations of the singlet states. We also compute excitation energies and zerofield splitting due to SOC and SSC, which agree with experiment. The numerical procedure we have developed is general, and so it can be applied to other point defects. 
Tuesday, March 16, 2021 10:24AM  10:36AM Live 
E32.00013: Optimal control and glassiness in quantum sensing Christopher Timms, Michael Kolodrubetz Qubits are known for being extremely responsive to their external environment, which has proven very beneficial in the domain of quantum sensing. These quantum sensors are very sensitive to small target fields; however, their sensitivity makes them highly prone to being disrupted by external noise. We simulate the use of quantum optimal control to control the qubits for sensing protocols. This allows us to maximize the effects of the target field on the qubit, while minimizing the effects of noise. Our work extends the pioneering results of Poggiali et al [PRX 8, 021059 (2018)] by allowing the use of non$\pi$ pulses. We find that this refinement results in both improved sensitivity as well as qualitative modifications of the control landscape. In particular, we investigate the ways in which the rough control landscape behaves as an analogue to a (classical) spin glass and comment on how this spin glass behavior can be applied to improve quantum sensing more broadly. 
Tuesday, March 16, 2021 10:36AM  10:48AM Live 
E32.00014: Accelerating axionic dark matter searches through remote entanglement of microwave cavities Yue Jiang, Elizabeth Ruddy, Benjamin M Brubaker, Kelly R Wurtz, Daniel A Palken, Konrad Lehnert Quantum metrology using superconducting circuits has found a natural application in the search for ultralight dark matter, in particular the QCD axion. The scan rate for cavitybased axionic dark matter searches is fundamentally limited by quantum noise. We propose a method to increase the scan rate using a twocavity setup, in which the axion cavity is coupled to an auxiliary readout cavity by simultaneous twomode squeezing and stateswapping interactions. We show analytically that by matching the rates of these interactions, we can achieve intracavity singlequadrature amplification of the axion signal before it is polluted by noise from outside the cavity, thereby increasing the scan rate by increasing tuning step size. This talk will discuss progress towards a prototype experiment in which we expect to achieve amplification corresponding to 20x scan rate enhancement and numerical modeling in the service of extending the concept to real operating haloscopes. 
Tuesday, March 16, 2021 10:48AM  11:00AM On Demand 
E32.00015: Singlemode quantum metrology enhanced by approximate quantum error correction Weiting Wang, Zijie Chen, Xinyu Liu, Weizhou Cai, Yuwei Ma, Ling Hu, Yuan Xu, Yipu Song, Haiyan Wang, Changling zou, Luyan Sun Quantum metrology makes use of quantum effects to achieve high measurement precision beyond classical limitations. However, in practice, quantum probe systems are sensitive to noise, restricting the attainable enhancement through quantum effects. In this talk, we will present our recent efforts in quantum metrology via a bosonic mode. We first show the principle of the singlemode bosonic quantum metrology with a superconducting circuit and demonstrate an unconditional phase estimation approaching the Heisenberg limit (HL). By preparing the superpositions of Fock states (0>+N>) up to N=12, we realize a 9.1 dB improvement over the SNL at N=12, which is only 1.7 dB away from the HL[1]. Then, we further extend our experimental architecture to fight against practical decoherence by introducing quantum error correction (QEC) technique to the bosonic mode. By an approximate QEC together with a trajectory method, we realize a photonnumber detection sensitivity on the order of 10^{4}HZ^{1/2}, achieving an enhancement over the case without any QEC technique. Our results reveal the considerable potential of bosonic QEC in quantum metrology applications. 
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