Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R07: Quantum Measurement and Sensing IIFocus

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Sponsoring Units: DQI Chair: HoiKwan Lau, University of Chicago Room: 102 
Thursday, March 5, 2020 8:00AM  8:12AM 
R07.00001: Optimal approximate quantum error correction for quantum metrology Sisi Zhou, Liang Jiang For a generic set of Markovian noise models, the estimation precision of a parameter associated with the Hamiltonian is limited by the 1/sqrt(t) scaling where t is the total probing time, in which case the maximal possible quantum improvement in the asymptotic limit of large t is restricted to a constant factor. However, situations arise where the constant factor improvement could be significant, yet no effective quantum strategies are known. Here we propose an optimal approximate quantum error correction (AQEC) strategy asymptotically saturating the precision lower bound in the most general adaptive parameter estimation scheme where arbitrary and frequent quantum controls are allowed. We also provide an efficient numerical algorithm finding the optimal code. Finally, we consider highlybiased noise and show that using the optimal AQEC strategy, strong noises are fully corrected, while the estimation precision depends only on the strength of weak noises in the limiting case. 
Thursday, March 5, 2020 8:12AM  8:24AM 
R07.00002: Multiparameter metrology with the Holevo Cramer Rao bound; an explicit 2qubit 3parameter bound Jamie Friel, Francesco Albarelli, Animesh Datta Quantum metrology is essential for the rigorous analysis and optimisation of all quantumlimited experiments. Since no experiment is ever truly a single parameter one what is required is multiparameter quantum metrology. It invokes the central axiom of quantum mechanics, that of incompatible observables. 
Thursday, March 5, 2020 8:24AM  8:36AM 
R07.00003: Parametricallyenhanced quantum sensing with effective nonHermitian lattice dynamics Alexander McDonald, Aashish Clerk Systems whose dynamics are described by a nonHermitian effective Hamiltonian have been suggested as platforms for improved sensing. Several experiments have already demonstrated the utility of exceptional points, a uniquely nonHermitian feature, in setups consisting of a few resonant modes [13]. The phenomena exhibited by coupled multimode nonHermitian systems, such as the nonHermitian skin effect [4] and the existence of abnormally large susceptibilities, are also promising sensing resources. Here, we show how to harness the unusual lattice physics to build quantum sensing platforms with remarkable properties. In particular, the quantum Fisher information of our measurement scheme grows exponentially with system size, even when bounding the number of photons used for the measurement. This is achieved without coupling to dissipative baths or postselection. Our setup is realizable in a number of experimental platforms, including superconducting quantum circuits and quantum optical setups. 
Thursday, March 5, 2020 8:36AM  8:48AM 
R07.00004: Metrology near exceptional points from superconducting circuits with loss Patrick Harrington, Maryam Abbasi, Yogesh Joglekar, Kater Murch The underlying mechanism of sensors, amplifiers, and metrological devices is a strong response to small perturbations. Such strong responses are expected for classical systems governed by nonHermitian Hamiltonians. We use postselection to create an effective nonHermitian Hamiltonian for a superconducting quantum circuit and measure the sensitivity of the circuit to a coherent drive for different system parameters. We find that the quantum Fischer information about the drive amplitude diverges at the exceptional point, indicating enhanced sensitivity. However, enhanced sensitivity is achieved at the cost of additional experimental data due to postselection statistics. With this experiment, we highlight the interplay of dissipation, dephasing, and loss near exceptional points of nonHermitian open quantum systems and, we observe the role of quantum measurement backaction for quantum sensing. 
Thursday, March 5, 2020 8:48AM  9:00AM 
R07.00005: Macroscopic Quantum Tunneling Devices for Nanoscale Attonewton Force Sensing Benjamin Safvati, YiTing Chen, Morgan Brubaker, Hari C. Manoharan The precision enabled by ultrahigh vacuum, low temperature scanning tunneling microscopy for atomic manipulation has allowed the design of nanostructures that exhibit quantifiable quantum dynamics. This work presents a novel nanoscale probe of atomicscale forces and enables new detection methods of the energy landscape in a Fermi gas. In a twodimensional electron gas, the geometry of the boundaries on the surface will produce uniquely nonlocal alterations in the electronic wave function. By creating a device in which a single atom or molecule can macroscopically tunnel between degenerate states in a double potential well, we are able to detect quantum forces that break the degeneracy by measuring an asymmetry in the tunneling rates between each side. Our new method of twodimensional nanoscale force measurement is able to detect forces with attonewton sensitivity, and the device’s design permits the probing of quantum forces due to proximal nanostructures with atomic resolution. Designer boundary conditions can amplify the measured forces and further illustrate the nonlocal nature of quantum force fields. We will discuss ways to extend device sensitivity even further, below the attonewton level. 
Thursday, March 5, 2020 9:00AM  9:12AM 
R07.00006: Dissipationbased quantum sensing of magnons Samuel Wolski, Dany LachanceQuirion, Yutaka Tabuchi, Shingo Kono, Koji Usami, Yasunobu Nakamura Magnons are the quanta of collective spin excitations. We introduce a novel technique for quantum sensing of magnons by leveraging the quantum coherence of a superconducting qubit which interacts with a magnetostatic mode. This is enabled by the realization of a strong dispersive coupling between the uniformly precessing magnetostatic mode in a ferromagnetic sphere and a superconducting qubit in a hybrid system [1,2]. A finite magnon population induces additional dephasing in the qubit, and can thus be inferred by probing the qubit coherence via Ramsey interferometry. A magnon detection sensitivitiy of around 10^{3 }magnons/√Hz is demonstrated, in good agreement with numerical simulations. The dissipationbased nature of our quantum sensor is confirmed by the dependence of the sensitivity on the detuning used in the Ramsey interferometry. The use of quantum sensing techniques in magnonics could find applications in fields such as magnon spintronics and magnetic field sensing. 
Thursday, March 5, 2020 9:12AM  9:24AM 
R07.00007: Quantum sensing with superconducting microwave circuits Matti Partanen, Kirill Fedorov, Stefan Pogorzalek, Michael Renger, QiMing Chen, Achim Marx, Frank Deppe, Rudolf O Gross Quantum mechanics offers intriguing opportunities for sensing applications with accuracies beyond the classically obtainable limits. An especially interesting approach is based on using entangled microwave photons for radar applications [Las Heras et al., Sci. Rep., 7, 9333 (2017)]. Here, we discuss a novel frequencydegenerate scheme for quantum sensing with superconducting microwave circuits. Our method is based on continuous variables that provide a convenient platform for quantum communication [Pogorzalek et al., Nat. Commun., 10, 2604 (2019)]. The same microwave regime is utilized in conventional radars owing to the transparency window of the atmosphere. Hence, our scheme suffers no conversion losses and, therefore, is promising for future realworld applications. 
Thursday, March 5, 2020 9:24AM  9:36AM 
R07.00008: QuantumEnhanced Noise Radar Nizar Messaoudi, Chung Wai Sandbo Chang, A.M. Vadiraj, Jerome Bourassa, Bhashyam Balaji, C.M. Wilson Quantum Illumination (QI) promises improvement in the sensitivity of target detection technologies. The approach takes advantage of strong correlations that can be created in electromagnetic beams using quantum processes, through a form of entanglement. Notably, QI has proven to be very robust to the presence of noise and loss, suggesting that it may have practical applications. We have made a proofofprinciple demonstration of a novel QI protocol: quantumenhanced noise radar (QENR). In QENR, we use a parametric amplifier to produce a twomode squeezed (TMS) state, which exhibits continuousvariable entanglement between signal and idler beams. This state is the input to the radar system. Compared to existing proposals for QI, our protocol does not require joint measurement of the signal and idler. This greatly enhances the practicality of the system by eliminating the need for a quantum memory to store the idler. We compare the performance of a TMS source to an ideal classical source that saturates the classical bound for correlation, finding a quantum enhancement approaching a factor of 10. One of the main challenges to making QENR practical is bringing the quantum microwaves out of the cryostat. We will discuss progress towards overcoming this challenge. 
Thursday, March 5, 2020 9:36AM  9:48AM 
R07.00009: Mitigating backaction in parametric quantum amplifiers Anja Metelmann, Archana Kamal Parametric quantum amplifiers are of paramount importance for quantum information processing with superconducting circuits. A promising route to design quantum amplifiers is based on parametric modulation of coupled modes, where the required modemixing processes are realized by utilizing Josephson junctionbased tunable couplers. All designs face the challenge of higherorder nonlinearities, resulting in a limitation of the dynamical range of the amplifier. However, even without any higherorder nonlinearities, the amplification process is itself nonlinear, e.g., it involves the mixing of three waves: the pump, the idler and the signal. Only for weak enough signal intensity the pump can be considered stiff and the amplification process becomes linear. Once the signal strength grows this approximation does not hold true anymore. The nonlinear nature of the mixing process leads to backaction, limiting the dynamical range of the amplifier. 
Thursday, March 5, 2020 9:48AM  10:00AM 
R07.00010: Near quantum limited Josephson traveling wave amplifiers I, Fabrication and characterization Luca Planat, Arpit Ranadive, Rémy Dassonneville, Javier Puertas, Sebastien Leger, Cécile Naud, Olivier Buisson, Wiebke Guichard, Denis M Basko, Nicolas Roch Efficient low noise amplification is a crucial component for any system dealing with low amplitude signals. Currently, Josephson parametric amplifiers(JPAs) can attain quantum limited amplification for microwave signals. However, JPAs based on resonant structures are limited to low bandwidth and saturation power. These limitations can be overcome using Josephson metamaterials forming traveling wave parametric amplifiers(TWPAs). 
Thursday, March 5, 2020 10:00AM  10:12AM 
R07.00011: Near quantum limited Josephson traveling wave amplifiers II
Performance and further development Arpit Ranadive, Luca Planat, Remy Dassonneville, Javier Puertas, Sebastien Leger, Cécile Naud, Olivier Buisson, Wiebke HaschGuichard, Denis M Basko, Nicolas Roch Efficient low noise amplification is a crucial component for any system dealing with low amplitude signals. Currently, Josephson parametric amplifiers(JPAs) can attain quantum limited amplification for microwave signals. However, JPAs based on resonant structures are limited to low bandwidth and saturation power. These limitations can be overcome using Josephson metamaterials forming traveling wave parametric amplifiers(TWPAs). 
Thursday, March 5, 2020 10:12AM  10:24AM 
R07.00012: Heisenberglimited singlemode quantum metrology in a superconducting circuit Weiting Wang, Yukai Wu, Yuwei Ma, Weizhou Cai, Ling Hu, Xianghao Mu, Yuan Xu, Zijie Chen, Haiyan Wang, Yipu Song, Haidong Yuan, Changling Zou, Luming Duan, Luyan Sun Quantum metrology is one of the most promising nearterm applications of quantum technology. Reaching a quantum advantage in metrology usually requires hardtoprepare twomode entangled states such as NOON states. Instead of exploring quantum entanglement in the twomode interferometers, a single bosonic mode also promises a measurement precision beyond the shotnoise limit (SNL) by taking advantage of the infinitedimensional Hilbert space of Fock states. In this talk, we demonstrate such a singlemode phase estimation that approaches the Heisenberg limit (HL) unconditionally in a superconducting circuit 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. Our experimental architecture can be combined with quantum error correction techniques to fight against decoherence, and thus promises quantumenhanced sensing in practical applications. 
Thursday, March 5, 2020 10:24AM  11:00AM 
R07.00013: Quantum Metrology in the Era of Quantum Information Invited Speaker: Rafal DemkowiczDobrzanski A comprehensive overview of the most recent advances in theoretical methods of quantum metrology will be presented, that in particular benefit from the quantum information related concepts such as quantum errorcorrection or matrix product states formalism. The theory developed allows to determine whether the Heisenberg scaling of precision is possible for a quantum sensor subject to a general Markovian noise. The theory takes into account all the possible quantum strategies, including entangling the sensor with ancillary systems, adaptive strategies such as e.g. quantum error correction protocols. Moreover, effective algorithms, based on the matrix product states/matrix product operator formalism, are developed that allow to identify the optimal metrological protocols in presence of noise (also correlated noise) in the limit of large number of probes, inaccessible by the stateoftheart methods. These results are highly relevant for modern developments of quantum enhanced sensing protocols, including NVcenter magnetometry, squeezed states enhanced optical and atomic interferometry or stabilization protocols for atomic clocks. 
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