Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session T67: ContinuousVariable Quantum Information: Resources and ApplicationsFocus

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Sponsoring Units: DQI Chair: David Roberts, University of Chicago Room: Room 412 
Thursday, March 9, 2023 11:30AM  11:42AM 
T67.00001: A novel nonGaussianity measure based on the Wigner entropy Andrew Pizzimenti, Christos N Gagatsos, Prajit Dhara, Zacharie Van Herstraeten, Sijie Cheng The enhanced phasespace characteristics of nonGaussian states of light, albeit necessary for universal quantum computing, render their understanding and production challenging. In attempts to circumvent these difficulties, several works have introduced nonGaussianity measures, i.e., quantities that assign a real number to states depending on their nonGaussian content (Genoni et al., 2007, 2008). Based on the Wigner entropy (Van Herstraeten & Cerf, 2021), we introduce a new measure μ[W], which is the Wigner relative entropy between an arbitrary Nmode state and its Gaussian associate defined as 
Thursday, March 9, 2023 11:42AM  11:54AM 
T67.00002: Quantum fDivergences via NussbaumSzkola distributions with applications to gaussian states George Androulakis, Tiju Cherian John We generalize the Nussbaum and Szkola distributions [Ann. Statist., vol. 37, no. 2, pp. 1040–1057, (2009)] to infinite dimensions, and we show that the quantum fdivergence of two quantum states on arbitrary dimensional Hilbert space is equal to the classical fdivergence of the corresponding NussbaumSzkola distributions. The method that we use for our derivation is the study of the spectral decomposition of the relative modular operator in a general setting. We give applications to gaussian states by studying a conjecture that was formulated by Seshadreeshan, Lami and Wilde [J. Math. Phys. 59, 072204 (2018)]. The talk is based on joint works with Tiju Cherian John. 
Thursday, March 9, 2023 11:54AM  12:06PM 
T67.00003: Understanding Quantum Supremacy Conditions for Gaussian Boson Sampling with High Performance Computing Minzhao Liu, Changhun Oh, Junyu Liu, Liang Jiang, Yuri Alexeev Recent quantum supremacy experiments demonstrated with boson sampling garnered significant attention, while efforts to perfect approximate classical simulation techniques challenge supremacy claims on different fronts. Singlephoton boson sampling has been proven to be efficiently simulable due to the limited growth of entanglement entropy, under the condition that the loss rate scales with the input photon number rapidly. However, similar studies for gaussian boson sampling remained difficult due to the increased Hilbert space dimensionality. We develop a graphical processing unitaccelerated algorithm and increase the algorithm parallelism to exploit highperformance computing resources, reducing the timetosolution significantly. With the new capability, we numerically observe similar entanglement entropy plateaus and reductions as input mode numbers increase under certain loss scalings. Additionally, we observe the nontrivial effects of squeezing parameters on entanglement entropy scaling. These new findings shed light on the conditions under which gaussian boson sampling is classically intractable.

Thursday, March 9, 2023 12:06PM  12:18PM 
T67.00004: Page curves and typical entanglement in linear optics Joseph T Iosue, Adam Ehrenberg, Dominik Hangleiter, Abhinav Deshpande, Alexey V Gorshkov Bosonic Gaussian states are a special class of quantum states in an infinite dimensional Hilbert space that are relevant to universal continuousvariable quantum computation as well as to nearterm quantum sampling tasks such as Gaussian Boson Sampling. In this work, we study entanglement within a set of squeezed modes that have been evolved by a random linear optical unitary. We first derive formulas that are asymptotically exact in the number of modes for the Rényi2 Page curve (the average Rényi2 entropy of a subsystem of a pure bosonic Gaussian state) and the corresponding Page correction (the average information of the subsystem) in certain squeezing regimes. We then prove various results on the typicality of entanglement as measured by the Rényi2 entropy by studying its variance. Using the aforementioned results for the Rényi2 entropy, we upper and lower bound the von Neumann entropy Page curve and prove certain regimes of entanglement typicality as measured by the von Neumann entropy. Our main proofs make use of a symmetry property obeyed by the average and the variance of the entropy that dramatically simplifies the averaging over unitaries. In this light, we propose future research directions where this symmetry might also be exploited. We conclude by discussing potential applications of our results and their generalizations to Gaussian Boson Sampling and to illuminating the relationship between entanglement and computational complexity. 
Thursday, March 9, 2023 12:18PM  12:30PM 
T67.00005: Multimode and Experimental Continuous Variable Shadow Tomography Srilekha Gandhari, Victor V Albert, Thomas Gerrits, Jacob M Taylor, Michael J Gullans Shadow tomography is a framework for constructing succinct descriptions of quantum states, called classical shadows, with powerful methods to bound the estimators used. Classical shadows are wellstudied in the discretevariable case, which consists of states of several qubits. Earlier, we extended this framework to continuousvariable (CV) quantum systems, such as optical modes and harmonic oscillators. Constraining the occupation number, such as the photonnumber for optical systems, to a maximum of N, we provided rigorous bounds on the sample complexity of singlemode states and applied our framework to existing optical tomography methods. 
Thursday, March 9, 2023 12:30PM  12:42PM 
T67.00006: Designbased continuous variable shadow tomography Joseph T Iosue, Kunal Sharma, Michael J Gullans, Victor V Albert Quantum state and unitary $t$designs play an important role in several applications, including tomography, randomized benchmarking, state discrimination, cryptography, sensing, and fundamental physics. In this work, we generalize the notion of state designs to infinitedimensional, separable Hilbert spaces. We first prove that under the definition of continuousvariable (CV) state $t$designs from [Comm. Math. Phys 326, 755771 (2014)], no state designs exist for $t geq 2$. Similarly, we prove that no CV unitary $t$designs exist for $t geq 2$. We propose an alternative definition for CV state designs, which we call rigged $t$designs, and provide explicit constructions for $t = 2$. As an application of rigged CV designs, we develop a protocol for the shadow tomography of CV states. We then regularize rigged $t$designs and construct energyconstrained CV state designs. Using regularizedrigged designs, we develop the notion of the average fidelity of a CV quantum channel. We provide an explicit formula for the average fidelity between an ideal displacement operation and its experimental approximation. Moreover, analogous to qudits, we establish a relationship between the average gate fidelity to entanglement fidelity for CV operations. 
Thursday, March 9, 2023 12:42PM  12:54PM 
T67.00007: Coherentstate quantum process tomography of continuousvariable gates in superconducting circuits Mikael Kervinen, Marina Kudra, Ahmed Shahnawaz, Axel M Eriksson, Fernando Quijandría, Anton F Kockum, Per Delsing, Simone Gasparinetti Encoding quantum information into a collection of a harmonic oscillator's Fock states shows a promising alternative towards universal quantum computing. Superpositions of multiple Fock states provide protection against errors at the cost of more complex quantum gates that address multiple Fock states simultaneously. Therefore, characterizing these gates becomes also more challenging. Here, we perform coherent state quantum process tomography (csQPT) for a continuousvariable superconducting circuit. CsQPT uses coherent states as input probes for the quantum process to completely characterize the quantum operation for an arbitrary input state. We show the results of this method by characterizing a quantum gate consisting of displacement and arbitrary phase (SNAP) operations on an encoded logical qubit. With this method we reconstruct the quantum process matrix for a large Hilbert space rather than being limited to the logical subspace. This allows for a more accurate determination of the various error mechanisms that lead to infidelity, and therefore can help in the diagnosis of the performance of continuousvariable quantum gates.

Thursday, March 9, 2023 12:54PM  1:06PM 
T67.00008: Multipartite continuousvariable entanglement generation using Josephson metamaterials Michael R Perelshtein The generation of quantum resources, most notably quantum entanglement, is an essential task for the new emerging industry employing quantum technologies. While entanglement in discrete variables represents the standard approach for quantum computing, continuous variable entanglement between microwave photons is a cornerstone for more robust quantum computing, sensing and communication schemes. 
Thursday, March 9, 2023 1:06PM  1:18PM 
T67.00009: Quantum Approximate Optimization Algorithm with Kerr resonators Pontus Vikstål The Quantum Approximate Optimization Algorithm (QAOA)one of the leading algorithms for applications on intermediatescale quantum processorsis designed to provide approximate solutions to combinatorial optimization problems with shallow quantum circuits. Here, we study QAOA implementations with Kerr resonators using qubits encoded into coherent states with opposite amplitudes. The dominant noise mechanism, i.e., photon losses, results in Zbiased noise with this encoding. We numerically show that running QAOA with Kerr qubits increases the approximation ratio for random instances of 8qubit MaxCut with respect to "standard" qubits encoded into twolevel systems, given the same average gate fidelities between the Kerr qubits and standard qubits. 
Thursday, March 9, 2023 1:18PM  1:54PM 
T67.00010: Quantum nonGaussian light and motion Invited Speaker: Radim Filip The talk will report our recent theoretical and experimental achievements opening the door to highly nonGaussian quantum physics with light and mechanical oscillators needed for quantum computation with continuous variables. This territory is challenging for investigation, both theoretically and experimentally. After briefly introducing the quantum nonGaussian effects for light (Phys. Rev. Lett. 123, 043601 (2019), Phys. Rev. Lett. 126, 213604 (2021)), we will present recent theoretical and experimental activities, including the faithful hierarchy of quantum nonGaussianity for multiphonon generation, its unpublished experimental verification and sensing capabilities Phys. Rev. Lett. 129, 013602 (2022)). Further, we will continue recent experimental results on generating quantum nonGaussianity of light from hot atomic ensembles (arXiv:2201.05366, accepted to npj Quant. Inf.). The talk will conclude with new unpublished results on nonGaussian quantum coherence, the following challenges in theory and experiments with light and mechanical oscillators to stimulate discussion and further development of this field. 
Thursday, March 9, 2023 1:54PM  2:06PM Author not Attending 
T67.00011: A physical graph representation of quantum optics experiments Xuemei Gu, Sören Arlt, Carlos Ruiz Gonzalez, Mario Krenn Graph theory is a very good abstract descriptive tool for modelling and explaining phenomena from physics. Progress has also taken place in recent years in the direction of applying graph theory in quantum experiments for state generation with probabilistic sources [13]. In this work, we will talk about a highly advanced connection between graph theory and quantum experiments which goes beyond the original representation, by showing that a colored weighted graph can capture all the information of a quantum optical experiment [4,5]. This new physical and abstract representation allow us to discover various quantum information tasks with current photonic technology, including highly entangled quantum states, quantum measurement schemes, quantum communication protocols, and multiparticle quantum gates. The graph can be translated back at any point to an experiment consisting of optical elements, and we explicitly show how to translate it into several quantum optical experiments. In general, our physical graphexperiment representation gives us a different perspective on photonic quantum technologies, and is significantly useful for the design of future quantum experiments and applications in quantum information [45]. 
Thursday, March 9, 2023 2:06PM  2:18PM Author not Attending 
T67.00012: Superconducting parametric cavity as an analog quantum simulator Dmytro Dubyna, Jamal Busnaina, Zheng Shi, Jimmy ShihChun Hung, Ibrahim Nsanzineza, Christopher Wilson Borrowing the concept of analog computers that simulated dynamics of complex classical systems in the era of embryonic digital computers, analog quantum simulators (AQSs) simulate dynamics of complex quantum systems while the emergence of fullscale quantum computer is yet to come. Our AQS is a superconducting quarterwave coplanar waveguide resonator which is terminated by an asymmetric Superconducting Quantum Interference Device (SQUID). An interaction between two cavity modes can be induced by a microwave pump with a frequency equal to either the sum or difference of two modes. Multiple pumps can be simultaneously applied to the same device, introducing multiple simultaneous couplings. This ability to control mode interactions in multimode device allows us to implement programmable photonic lattices by arranging mode connections in synthetic dimensions. The properties of the simulated model can be revealed through transmission and scattering measurements of the lattice sites. Thus, we successfully simulated the bosonic Creutz ladder [1] and now we demonstrate the simulation of the SuSchrieffer–Heeger (SSH) model, both of which are paradigmatic topological models. In the SSH lattice, we realize different topological states depending on the intercellintracell coupling ratio and the parity of the sites in the lattice. We will also present preliminary measurements of injecting nonclassical microwave states into the SSH lattice. 
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