Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N35: General Quantum Information IIRecordings Available
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Sponsoring Units: DQI Chair: Chenxu Liu, Virginia Tech Room: McCormick Place W-193B |
Wednesday, March 16, 2022 11:30AM - 11:42AM |
N35.00001: Semiclassical Approach to Self-Consistent Classical-Quantum Coupling Ilon Joseph, Alessandro R Castelli, Vasily I Geyko, Frank R Graziani, Stephen B Libby, Roger W Minich, Max D Porter, Yuan Shi, Jonathan L DuBois A self-consistent coupling of classical and quantum subsystems that correctly predicts backreaction effects is derived for the first time by considering a bipartite quantum system and taking the semiclassical large quantum number limit for one of the subsystems. This approach results in a configuration space version of the Koopman-van Hove Hamiltonian [1-3] for the coupled system and is equivalent to an operator-valued version of WKB theory. Injecting the configuration space dynamics into classical phase space yields a straightforward proof of the recently proposed methodology in [1]. However, the semiclassical version has different boundary conditions than the classical version that improve accuracy by generating "quantum" effects such as interference, the Einstein-Brillouin-Keller quantization conditions, and tunneling through classically forbidden regions. While the configuration space version is nonlinear, the phase space version is both linear and unitary which enables the possibility of simulating semiclassical dynamics on quantum computers. |
Wednesday, March 16, 2022 11:42AM - 11:54AM |
N35.00002: Quantum simulation of excited states with the transcorrrelated Hamiltonian: higher accuracy with fewer qubits Ashutosh Kumar, Yu Zhang, Pavel A Dub, Sergei Tretiak In this work, we use the canonical transcorrelated theory to construct effective and compact molecular Hamiltonians, which can make accurate quantum simulation of ground and excited states on Noisy Intermediate-Scaling Quantum (NISQ) devices much cheaper. This approach involves a unitary transformation of the Hamiltonian with a geminal F12 operator which is a function of the inter-electronic distances. The coulomb singularities appearing in the regular Hamiltonian is removed after this procedure, as a result of which, any many-body method (UCC, FCI) with this effective Hamiltonian requires a fewer number of qubits to obtain accurate energies. We tested this approach for simulating ground states of small molecules earlier (Phys. Chem. Chem. Phys., 2020, 22, 24270-24281) and got very encouraging results which motivated us to consider excited states as well. Since, excited states are usually much more entangled than ground states, the Hamiltonian needs to be dressed with generalized geminal excitation operators unlike quasi-double geminal excitations that we used for the ground state simulation. This approach enables us to drastically reduce the number of qubits and circuit depth while maintaining the desired accuracy for both ground and excited-state properties. |
Wednesday, March 16, 2022 11:54AM - 12:06PM |
N35.00003: Quantum state reconstruction with biased distributions of quantum states Sanjaya Lohani, Joseph M Lukens, Daniel E Jones, Thomas A Searles, Ryan T Glasser, Brian T Kirby We consider the properties of a specific distribution of mixed quantum states of arbitrary dimension that can be biased towards a specific mean purity. In particular, we analyze mixtures of Haar-random pure states with Dirichlet-distributed coefficients. We analytically derive the concentration parameters required to match the mean purity of the Bures and Hilbert--Schmidt distributions in any dimension. Numerical simulations suggest that this value recovers the Hilbert--Schmidt distribution exactly, offering an alternative and intuitive physical interpretation for ensembles of Hilbert--Schmidt-distributed random quantum states. We then demonstrate how substituting these Dirichlet-weighted Haar mixtures in place of the Bures and Hilbert--Schmidt distributions results in measurable performance advantages in machine-learning-based quantum state tomography systems and Bayesian quantum state reconstruction. Finally, we experimentally characterize the distribution of quantum states generated by both a cloud-accessed IBM quantum computer and an in-house source of polarization-entangled photons. In each case, our method can more closely match the underlying distribution than either Bures or Hilbert--Schmidt distributed states for various experimental conditions. |
Wednesday, March 16, 2022 12:06PM - 12:18PM |
N35.00004: Quantum phase transitions in entanglement complexity in Rokhsar-Kivelson-type wave functions Stefano Piemontese, Alioscia Hamma We study the behavior of families of states in the Rokhsar-Kivelson form under the Metropolis entanglement cooling algorithm introduced in [1]. We show the existence of two quantum phases. In the disordered phase, the algorithm is completely incapable of disentangling, thus revealing a complex pattern of entanglement, while in the ordered phase a finite amount of disentanglement is possible. We construct an order parameter from the relative effective disentangling performance and show an order-disorder quantum phase transition with universal critical indexes. In addition, we show that the disordered phase has complex pattern of entanglement as revealed by the Wigner-Dyson distribution for the gaps in the entanglement spectrum of Haar-random matrices. In contrast, states in the ordered phase stray away from the universal distribution. |
Wednesday, March 16, 2022 12:18PM - 12:30PM |
N35.00005: Analytical framework for describing non-trivial quantum dissipation Zhihao Xiao, Nicolas Diaz Naufal, Andrew Keefe, Anja Metelmann, Archana Kamal Recent works have shown how quantum correlations can be harnessed for Hamiltonian amplification in cavity-QED and circuit-QED setups. However, interplay of such correlations with noise still remains an active area of study. Specifically driven-dissipative dynamics of a system, coupled to a reservoir with strong correlations, remains insufficiently understood. This is partly due to the fact that well-established methods such as adiabatic elimination need to be revisited in the presence of strongly correlated quantum reservoirs. In this talk, we will present the progress towards a self-consistent derivation of quantum master equation in the presence of strong quantum correlations. Applying it to quantum reservoir with Gaussian correlations, we will first discuss how both the effective Hamiltonian and dissipator get modified. Using exact simulations to benchmark the analytical description of the reduced system, we will then comment on the implications of reservoir correlations on the validity of adiabatic elimination. |
Wednesday, March 16, 2022 12:30PM - 12:42PM |
N35.00006: Quantum Steganography using Coherent states in an Optical Channel Bruno Avritzer, Todd A Brun Quantum Steganography is a class of methods for covert quantum communication which take advantage of an information gap between the eavesdropper and the communicating parties to send information secretly. Challenges in this area include finding viable methods and optimizing them for the best possible communication rate. In this talk we outline several procedures by which one might communicate covertly in this manner by encoding messages in coherent state mixtures that would appear as a thermal background to eavesdroppers, calculate the efficiency of such procedures in optical systems, and describe their potential implementation and effectiveness on actual quantum hardware using homodyne measurement schemes. |
Wednesday, March 16, 2022 12:42PM - 12:54PM |
N35.00007: Quantum state driving: measurements versus pulses Yi-Hsiang Chen The quantum Zeno effect is well-known for fixing a system to an eigenstate by frequent measurements. It is also known that applying frequent unitary pulses induces a Zeno subspace that can also pin the system to an eigenspace. Both approaches have been studied as means to maintain a system in a certain subspace. Extending the two concepts, we consider making the measurements/pulses dynamical so that the state can move with the motion of the measurement axis/pulse basis. We show that the system stays in the dynamical eigenbasis when the measurements/pulses are slowly changing. Explicit bounds for the apply rate that guarantees a success probability are provided. In addition, both methods are inherently resilient against non-Markovian noise. Finally, we discuss the similarities and differences between the two methods and their connection to adiabatic quantum computation. |
Wednesday, March 16, 2022 12:54PM - 1:06PM |
N35.00008: PT-symmetric holographic principle: applying non-Hermitian quantum evolution to quantum simulation Xingrui Song, Kater W Murch Originating from the Hamiltonian of a single qubit system, the phenomenon of the avoided level crossing is ubiquitous in multiple branches of physics, including the Landau-Zener transition in atomic, molecular and optical physics, the band structure of condensed matter physics, and the dispersion relation of relativistic quantum physics. We revisit this fundamental phenomenon in the simple example of a spinless relativistic quantum particle traveling in (1+1)-dimensional space-time and establish its relation to a spin-1/2 system evolving under a PT-symmetric Hamiltonian. This relation allows us to simulate a 1D scattering problem with a single qubit. We summarize and generalize this type of relation as the eigenenergy problem of a bulk system with N spatial dimensions being mapped onto the time evolution of the edge state with (N-1) spatial dimensions governed by a non-Hermitian Hamiltonian. In other words, the bulk eigenenergy state is encoded in the edge state as a hologram, which can be decoded by the propagation of the edge state in the remaining one spatial dimension. We further conjecture that a majority of such evolution will be PT-symmetric as long as the bulk system admits the symmetry transformation of 180-degree rotation. Our work finds the application of PT-symmetric and non-Hermitian physics in quantum simulation and provides insights into the fundamental symmetries. |
Wednesday, March 16, 2022 1:06PM - 1:18PM |
N35.00009: Predicting many properties of quantum systems with chaotic dynamics Soonwon Choi, Yizhuang You We generalize the classical shadow tomography scheme to a broad class of finite-depth or finitetime local unitary ensembles, known as locally scrambled quantum dynamics, where the unitary ensemble is invariant under local basis transformations. In this case, the reconstruction map for the classical shadow tomography depends only on the average entanglement feature of classical snapshots. We provide an unbiased estimator of the quantum state as a linear combination of reduced classical snapshots in all subsystems, where the combination coefficients are solely determined by the entanglement feature. We also bound the number of experimental measurements required for the tomography scheme, so-called sample complexity, by formulating the operator shadow norm in the entanglement feature formalism. We numerically demonstrate our approach for finite-depth local unitary circuits and finite-time local-Hamiltonian generated evolutions. The shallow-circuit measurement can achieve a lower tomography complexity compared to the existing method based on Pauli or Clifford measurements. Our approach is also applicable to approximately locally scrambled unitary ensembles with a controllable bias that vanishes quickly. Surprisingly, we find a single instance of time-dependent local Hamiltonian evolution is sufficient to perform an approximate tomography as we numerically demonstrate it using a paradigmatic spin chain Hamiltonian modeled after trapped ion or Rydberg atom quantum simulators. Our approach significantly broadens the application of classical shadow tomography on near-term quantum devices. |
Wednesday, March 16, 2022 1:18PM - 1:30PM |
N35.00010: Stochastic Semi-Classical Models of Operator Front Dynamics Sridhar Prabhu, Yuri Lensky, Debanjan Chowdhury The growth in size and complexity of generic local operators due to unitary time evolution has been studied for numerous quantum models and using a variety of theoretical techniques. The operator-front spreads ballistically, and in the limit of late times has a universal "hydrodynamic" description. For a class of quantum models, we provide evidence for an effective classical description of this hydrodynamic behavior that can be simulated efficiently using models of "cellular automata" (CA). Starting with a few elementary CA rules we demonstrate the emergence of distinct universality classes of operator-front hydrodynamics, which leads to complementary insight into the dynamics of quantum many-body systems. |
Wednesday, March 16, 2022 1:30PM - 1:42PM |
N35.00011: Role of Coherence and Degeneracies in Quantum Synchronisation Sai Vinjanampathy, Noufal Jaseem, Michal Hajdušek, Parvinder Solanki Progress on the study of synchronisation in quantum systems has been largely driven by specific examples which resulted in several examples of frequency entrainment as well as mutual synchronisation. Here we study quantum synchronisation by utilising Liouville space perturbation theory. We begin by clarifying the role of centers, symmetries and oscillating coherences in the context of quantum synchronisation. We then analyse the eigenspectrum of the Liouville superoperator generating the dynamics of the quantum system and determine the conditions under which synchronisation arises. We apply our framework to derive a powerful relationship between energy conservation, degeneracies and synchronisation in quantum systems. Finally, we demonstrate our approach by analysing two mutually coupled thermal machines and the close relationship between synchronisation and thermodynamic quantities. |
Wednesday, March 16, 2022 1:42PM - 1:54PM |
N35.00012: Exact mean root fidelity and mean-square Bures distance between random density matrices Aritra Laha, Agrim Aggarwal, Santosh Kumar Distance measures between quantum states play a crucial role in various aspects of quantum information theory and have applications in a variety of physical problems. Among various distance measures, Bures distance stands out as an excellent candidate for distinguishability measures between quantum states due to its several notable features. In this work, we derived exact analytical results for the mean root fidelity and the mean-square Bures distance using the random matrix theory (RMT) techniques for the pairs of a fixed density matrix and a random density matrix, and two random density matrices, taken from the Hilbert-Schmidt probability measure. The key idea of our calculation was to reformulate the problems in terms of known RMT ensembles with the aid of the Laplace transform approach. We also obtained the spectral density for the product of the above-mentioned pairs of density matrices. We compared our random matrix theory-based analytical results with Monte-Carlo-based numerical simulations and found excellent agreement. Additionally, we corroborated these analytical results by contrasting them with the mean square Bures distance between random density matrices generated via coupled kicked tops. |
Wednesday, March 16, 2022 1:54PM - 2:06PM |
N35.00013: Rewinding time with photons Teodor Strömberg, Miguel Navascues, David Trillo, Benjamin Dive, Valeria Saggio, Peter Schiansky, Philip Walther We present and experimentally implement a universal rewinding protocol for two-level quantum systems. The protocol takes an unknown quantum state, evolving under an unknown Hamiltonian, and brings it back to its initial state. Unlike previous known time-translation protocols, ours can achieve an arbitrarily high probability of success, and is furthermore asymptotically optimal in the sense that it only requires O(T) amount of time to rewind the system by T units of time. Our experimental demonstration applies the protocol to qubits encoded in the polarization degree of photons, where the time evolution under a Hamiltonian for time ΔT is mimicked by applying the corresponding unitary operator. We compare our results to a classical strategy and find that the quantum protocol achieves a dramatically higher fidelity that is independent of choice of initial state, Hamiltonian and length of time to be rewound. |
Wednesday, March 16, 2022 2:06PM - 2:18PM |
N35.00014: Quantum computers to test fundamental physics or viceversa Lorenzo Maccone, Urbasi Sinha, Simanraj Sadana We present two complementary viewpoints for combining quantum |
Wednesday, March 16, 2022 2:18PM - 2:30PM |
N35.00015: Experimental test of no-collapse Quantum Mechanics: Are there quantum "Dark States"? Shahriar Afshar We investigate the nature of wavefunction (WF) collapse in a welcher weg experiment by observing the physical effects of the so-called empty waves (EWs), more specifically their ability to interfere with real photons to generate first order interference. We spatially superpose the EW of an already-detected photon with the temporally-separated WF of a second photon. We achieve this by sending very weak highly coherent pulses of light into an asymmetrical MZI. To ensure overlap, repetition rate of pulses is set to f = c/OPD, c being speed of light in the medium and OPD the optical path difference (OPD). Both long and short arms have an additional interrogator beamsplitter early in each path so that interrogator photon detectors (IPDs) can detect presence of a photon in each arm. Due to the Poissonian statistics of coherent light, occasionally a photon and an EW arrive at the final BS together, temporally separated by ΔT = OPD/c. Coincidence rate of IPDs and a detector at one of the final BS outputs is measured. Observation of change in coincidence rates that corresponds to interference phenomena would violate the Copenhagen and MW Interpretations. Finally the novel concept of “Quantum Dark States” (D-states) will be introduced as potential cause of observed Cosmological Constant. |
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