Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S28: Quantum Measurement and Sensing IIIFocus

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Sponsoring Units: DQI Chair: Lucas Sletten, University of Colorado, Boulder Room: BCEC 161 
Thursday, March 7, 2019 11:15AM  11:27AM 
S28.00001: Role of nonclassical correlations in quantum parameter estimation assisted by a local measurement scheme in thermal equilibrium Akira Sone, Quntao Zhuang, Changhao Li, YiXiang Liu, Paola Cappellaro We discuss the role of nonclassical correlations in enhancing estimation sensitivity of parameters characterizing the quantum system in thermal equilibrium, in terms of greedy local measurement scheme, where subsystems are measured sequentially with the local optimal measurements. We introduce a practical discord, called discord for local metrology, to measure the nonclassical correlations induced by local optimal measurement, and we explicitly derive its relation to loss in quantum Fisher information in the hightemperature limit. We also demonstrate that discord for local metrology becomes diagonal discord when the estimated parameter is linearly coupled to the Hamiltonian. Practically, this result in the hightemperature limit could provide a measurement or control strategy to utilize nonclassical correlations to achieve a precise sensing or imaging in roomtemperature NMR system or living cells. 
Thursday, March 7, 2019 11:27AM  11:39AM 
S28.00002: Supersensitive Metrology using Induced Coherence William Plick, Nathaniel R Miller We theoretically analyze the phase sensitivity of the wellknown ``InducedCoherence Interferometer'', including the case where the sensitivity is ``boosted'' into the subshotnoiselimit regime with coherentlight seeding. We find scaling which reaches below the standard quantum limit, even when seeding the spatial mode which does not interact with the sample. This allows bright, supersensitive phase estimation of an object with different light fields for interaction and detection, with various potential applications, especially in cases where the sample may be sensitive to light or is most interesting in frequency domains outside what is easily detected. It is a hybrid of a linear and nonlinear interferometers, and aside from the supersensitivity, is distinguished from other systems by ``preferring'' an imbalance in the gains of the two nonlinearities, and nonmonotonic behavior of the sensitivity as a function of the gain of the coherenceinducing medium. We use an analysis in terms of general squeezing and show that supersensitivity occurs only in this case  that is, the effect is not present in the spontaneousparametricdownconversion regime, which previous analyses and experiments have focused on. 
Thursday, March 7, 2019 11:39AM  11:51AM 
S28.00003: Oxygenated (113) diamond surface for nitrogenvacancy quantum sensors with preferential alignment and long coherence time from first principles SONG LI, JyhPin Chou, Jie Wei, Minglei Sun, Alice Hu, Adam Gali Shallow nitrogenvacancy (NV) center in diamond is promising in quantum sensing applications however its sensitivity has been limited by surface terminators and defects. There is an immediate quest to find suitable diamond surfaces for NV sensors. In this work, the surface terminators of (113) diamond to host shallow NV centers are studied by means of first principles calculations. Results indicate that complete oxygen termination of (113) diamond creates positive electron affinity with no surface states ingap levels. Combining this with the ~73% preferential alignment of asgrown NV centers in (113) oriented diamond, oxygenated (113) diamond is presently supposed to be the most prospective host for NV quantum sensors. 
Thursday, March 7, 2019 11:51AM  12:03PM 
S28.00004: Quantumenhanced rotation measurements – a multiparameter problem Aaron Goldberg, Daniel James Precise rotation measurements have numerous classical and quantum applications. Particular quantum states can be used to dramatically increase sensitivities in estimating rotation angles around a known axis. We present a class of states that offer similar enhanced sensitivities in estimating both the orientation of an unknown rotation axis and the angle rotated about it. We derive a quantum CramérRao bound for simultaneously estimating the three Euler angles of a rotation and discuss states that achieve Heisenberglimited sensitivities for all three. Our states are "anticoherent" states, for whose identification we provide new geometric insights. This result is immediately useful for shotnoiselimited metrology. 
Thursday, March 7, 2019 12:03PM  12:15PM 
S28.00005: Detecting Macroscopic Indefiniteness of Cat States in Bosonic Interferometers Shane Kelly, Eddy M.E. Timmermans, ShanWen Tsai The paradigm of Schrodinger’s cat illustrates how specific superposition states preclude the assignment of definite properties to a macroscopic object (realism). In this work we develop a method to investigate the indefiniteness of cat states using currently available cold atom technology. The method we propose, uses observation of a statistical distribution to demonstrate the macroscopic distinction between dead and alive states and the interferometric sensitivity(Fisher Information) to detect the indefiniteness of the vital status of the cat. We show how these two observations can provide information about the quantum state without full quantum state tomagraphy. We test this method using a cat state proposed by Gordon et. al.(PRA 59 4623), which is dynamically produced from a coherent state. As a control, we consider a set of states produced using the same dynamical procedure acting on an initial thermal distribution. Numerically simulating our proposed method, we show that as the temperature of this initial state is increased, the produced state undergoes a quantum to classical crossover where the indefiniteness of the vital status of the is lost, while the macroscopic distinction between dead and alive states of the cat is maintained. 
Thursday, March 7, 2019 12:15PM  12:27PM 
S28.00006: Optimal Estimation of Complex Squeezing in Phase Space Jasminder Sidhu, Pieter Kok All optical fields fluctuate in both phase and amplitude due to stochastic indeterminacy, which imposes a fundamental shot noise uncertainty to measurements. Squeezed states surpass this precision limit in one quadrature at the expense of a concomitant increased uncertainty to the complementary quadrature. These states are heavily used in continuous variable quantum information processing [1], quantum metrology [2], and optical quantum computing. Full characterisation of the squeezed states used is required to envisage the progression of these applications. 
Thursday, March 7, 2019 12:27PM  12:39PM 
S28.00007: Minimal quantum state representations from denoising autoencoders Shiva Lotfallahzadeh Barzili, Razieh Mohseninia, Justin Dressel As multiqubit systems increase in size, the state space scales exponentially. This makes accurate state tomography increasingly challenging and places a high demand on computational resources. This problem is compounded by the addition of experimental noise in tomographic measurements. We investigate the use of supervised machine learning, in the form of modified denoising autoencoders, to simultaneously remove experimental noise while finding minimal latent representations of the quantum state. These representations can be later decoded into more traditional state representations. 
Thursday, March 7, 2019 12:39PM  12:51PM 
S28.00008: An implementation of the generalized coherentstate measurements Christopher Jackson Generalized coherentstates are a beautiful theoretical tool for describing quantum systems with Lie group symmetries. The POVM of projectors onto the continuum of generalized coherentstates is also known to be the optimal measurement for estimating unknown states given multiple copies. However, it has been thought that this POVM is in general not practical to realize. We show how one can in principle realize this POVM by a sequence of isotropic weak measurements. 
Thursday, March 7, 2019 12:51PM  1:03PM 
S28.00009: Detecting Dark Matter with Polar Materials using ab initio calculations. Sinead Griffin, Simon Knapen, Tongyan Lin, Kathryn M Zurek Dark matter (DM) comprises ~25% of the massenergy density of the universe, yet to date has eluded direct detection. Ultralight DM has emerged as a promising possibility for DM, and is only now becoming experimentally viable for direct searches. In this work we propose the direct detection of DM with polar materials, considering both the scattering of optical and acoustic phonons by light DM, and the absorption of dark photons by optical phonons. Using Density Functional Theory, we calculate the materialspecific matrix elements, and show that DM scattering in an anisotropic crystal has a strong directional dependence. We find that phononbased detectors have comparable or greater sensitivity to subMeV dark matter scattering and subeV dark matter absorption than other current proposals. 
Thursday, March 7, 2019 1:03PM  1:15PM 
S28.00010: Longliving coherence in 2D and 3D disordered dipolarcoupled spin systems under strong periodic driving Viatcheslav Dobrovitski, Walter Hahn It has been found recently [1] that a 3D dipolarcoupled network of electronic spins under periodic driving shows longliving coherence and signatures of the timecrystallike order. Similar behavior has also been observed and studied before [2,3], in the 3D networks of the nuclear spins subjected to the spinecho pulse trains, and has been used for 70,000fold improvement in NMR spectroscopy [2]. 
Thursday, March 7, 2019 1:15PM  1:27PM 
S28.00011: Results and model for singlegate ratchet charge pumping Neil Zimmerman, Roy Murray, Justin K Perron, Michael David Stewart, Masaya Kataoka, Stephen Giblin, Jonathan Fletcher Singlegate ratchet pumping is based on a Brownian motor mode, and thus can present subtle behavior. We show experimentally that, in the same devices, we can demonstrate multiple twogate pumping modes but not the singlegate mode. We propose three mechanisms to explain the lack of plateaus in the singlegate ratchet mode: a large plungertobarrier ratio compared to the charging energy (Δptb/EC), nonlinear tunnel barriers, and phase offset leading to nonequilibrium heating. Our analysis shows that each of these could contribute to the lack of plateaus in the 1gate ratchet pumping, but allow 2gate pumping methods to work with robust plateaus. We propose several methods to reduce these sources of error, including reducing gate oxide thickness and reducing cross capacitances. 
Thursday, March 7, 2019 1:27PM  1:39PM 
S28.00012: Superparamagnetic reversal of single magnetic nanoparticles near phase transition Ning Wang, Weng Hang Leong, GangQin Liu, Xi Feng, Chufeng Liu, Sen Yang, Joerg Wrachtrup, Quan Li, Renbao Liu The magnetic properties of single magnetic nanoparticles, especially the superparamagnetic (SPM) reversal near the phase transition point, are relevant to information storage, biomedicine imaging, and paleology. However, it is challenging to study the SPM reversal of single nanoparticles due to the weak magnetic moment and the sharp temperature dependence of the reversal rate. Here, we utilize nitrogenvacancy centers in diamond as a quantum probe to study the SPM reversal of individual magnetic particles. Such a configuration enables the verification of the NeelArrhenius law and the StonerWohlfarth model at the singleparticle level. We observe that the reversal rate changes from 10^{2} Hz to 10^{4} Hz in approximate 10 K temperature range. The SPM reversal rate as a function of temperature indicates that the NeelArrhenius law is still valid when the temperature is 1/20 Tc close to the Curie temperature of the magnetic nanoparticle. 
Thursday, March 7, 2019 1:39PM  1:51PM 
S28.00013: Quantum information measures of the AharonovBohm ring in uniform magnetic fields Oleg Olendski Shannon quantum information entropies S_{ρ,γ}, Fisher informations I_{ρ,γ} and Onicescu energies O_{ρ,γ} are calculated in the position (subscript ρ) and momentum (subscript γ) spaces for the azimuthally symmetric 2D nanoring that is placed into the combintaion of the transverse uniform magnetic field B and AharonovBohm (AB) flux Φ. Position (momentum) Shannon entropy depends on the field as negative (positive) logarithm of ω_{eff}=(ω_{0}^{2}+ω_{c}^{2}/4)^{1/2}, with ω_{c }being cylcotron frequency, what makes the sum S_{ρ}+S_{γ} a fieldindependent quantity that increases with the principal n and aizmuthal m quantum numbers and satisfies entropic uncertainty relation. Position Fisher information does not depend on m, linearly increases with n and varies as ω_{eff }whereas its Onicescu counterpart changes as 1/ω_{eff}. The products I_{ρ}I_{γ and }O_{ρ}O_{γ} are both Bindependent quantities. Dependence of the measures on the thickness of the ring is discussed. It is shown that position Shannon entropy has the same dependence on the AB flux Φ as the energy spectrum. Other analytic and numerical results for all measures are discussed too and their physical meaning is highlighted. 
Thursday, March 7, 2019 1:51PM  2:03PM 
S28.00014: Electron spin coherence measurements of highdensity silicon vacancy ensembles in silicon carbide John Abraham, Jacob Epstein, Jeremiah Wathen High density ensembles of defects in solids hold the potential to realize highly correlated states or high sensitivity quantum sensors. To explore the feasibility of this development path for silicon vacancies in silicon carbide, we will present electron spin coherence measurements of neutron irradiated samples of silicon carbide. To date, published measurements of the electron spin coherence time of this system have primarily been with electron or proton irradiated samples where the density of defects is not uniform throughout the sample. Since the density of defects is uniform throughout the sample with neutron irradiation, these measurements will shed light regarding the observed anomalies (Phys. Rev. B 95, 045206 (2017)) in the density dependence of the spin coherence time with silicon vacancy ensembles. 
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