Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S31: Generating and Characterizing Continuous Variable Quantum ResourcesFocus Live
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Sponsoring Units: DQI Chair: David Roberts, University of Chicago |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S31.00001: Gaussian conversion protocols for cubic phase state generation: Part 1 Oliver Hahn, Yu Zheng, Pascal Stadler, Patric Holmvall, Isaac Quijandria Diaz, Alessandro Ferraro, Giulia Ferrini Universal quantum computing with continuous variables requires non-Gaussian resources, in addition to a Gaussian set of operations. A known resource enabling universal quantum computation is the cubic phase state, a non-Gaussian state whose experimental implementation has so far remained elusive. |
Thursday, March 18, 2021 11:42AM - 11:54AM Live |
S31.00002: Gaussian conversion protocols for cubic phase state generation: Part 2 Yu Zheng, Oliver Hahn, Pascal Stadler, Patric Holmvall, Isaac Quijandria Diaz, Alessandro Ferraro, Giulia Ferrini In order to achieve universality in quantum computation with continuous-variable systems, cubic phase states play a crucial role, as they can promote a Gaussian set of operations to universal quantum computation. The generation of these states has however been challenging in quantum optics, due to the weakness of the non-linearities that are typically available in that domain. In this talk, we introduce a probabilistic Gaussian conversion protocol that allows one to prepare a cubic phase state by starting from a trisqueezed state that has been realized experimentally with microwave circuits [Sandbo Chang et al., Phys.Rev. X10, 011011 (2020)], and using Gaussian operations and measurement. The measurement is conditioned on a specific outcome, which renders the protocol probabilistic. We analyze the performance of our conversion protocol in terms of fidelity of conversion and success probability. Furthermore, we show that our probabilistic conversion protocol allows for achieving a higher conversion fidelity, as compared to the fidelity achievable with deterministic Gaussianconversion protocols. |
Thursday, March 18, 2021 11:54AM - 12:06PM Live |
S31.00003: Robustness of deformed catlike states under dissipative decoherence Abdessamad Belfakir The generation of coherent superposition of distinct physical systems and the construction of robust entangled states under decoherence are the most experimental challenges of quantum technologies. In a recent work [1], we have investigated the behaviors of catlike states of a deformed harmonic oscillator under dissipative decoherence. Varying the deformation parameters, we have obtained catlike states having more resistance against decoherence than catlike states of the ordinary harmonic oscillator. Furthermore, we have studied nonclassical properties and entanglement of different catlike states subjects to decoherence caused by a dissipative interaction with a large environment. Depending on different parameters of deformation, we have shown that the nonclassical properties of catlike states under dissipative interaction can be more retarded and preserved in the time [1]. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S31.00004: Wigner negativity in the steady-state output of a Kerr parametric oscillator Ingrid Strandberg, Göran Johansson, Isaac Quijandria Diaz A quantum mechanical state can be fully characterized in phase space by its Wigner function. Unlike a proper probability distribution which is always positive, the Wigner function can take negative values in some regions of phase space. This is indicative of nonclassicality, and quantum states with a negative Wigner functions can be useful resources for quantum computing. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S31.00005: Robust engineering of universal Gaussian cluster states in harmonic lattices with a single-site squeezed reservoir David Vitali, Stefano Zippilli We first show that any Gaussian cluster state of N bosonic modes can be generated by a multi-mode squeezing transformation. and provide the explicit recipe. We then use this result to show that a large class of pure entangled CV Gaussian states, including 2D-cluster states, can be robustly generated as unique steady state of a dissipative dynamics employing minimal resources. In fact, this is achievable using only a single-site squeezed driving and passive bilinear interactions. We provide the explicit protocol which corresponds to the engineering of a suitable excitation number conserving Hamiltonian.This fact can be used for the implementation of universal continuous variable measurement-based-quantum computation on various platforms. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S31.00006: Constraints on Gaussian error channels for entanglement swapping with Gaussian measurements Alex Kwiatkowski, Ezad Shojaee, Sristy Agrawal, Scott Glancy, Emanuel Knill We describe a formalism for Gaussian measurements of continuous-variable quantum systems and use it to derive constraints on entanglement swapping. First, we consider a two-mode entangled Gaussian measurement preceded by independent attenuation channels on the two modes and show that if the sum of the attenuations exceeds 1 then any Gaussian measurement becomes separable and therefore unsuitable for entanglement swapping. We then use a well-known classification of single-mode Gaussian channels to extend this constraint to all pairs of single-mode Gaussian error channels. Finally, we show that our constraints are tight, meaning that Gaussian entanglement swapping is possible if and only if the pair of error channels meets the required constraints. |
Thursday, March 18, 2021 12:42PM - 1:18PM Live |
S31.00007: Non-Gaussian quantum states of a multimode light field Invited Speaker: Nicolas Treps Wigner functions that take negative values are considered to be a crucial resource for achieving a quantum computational advantage with continuous variables. In quantum optics, the subtraction (or addition) of a photon from a squeezed state is a common method to generate such Wigner-negativity [1]. But this process has to be made mode-dependent with a multimode environment to prove useful for quantum information. For instance, it was shown that photon subtraction in one mode induces non-Gaussian properties in the modes that are correlated to it [2]. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S31.00008: Generation of Gottesman-Kitaev-Preskill codes in a periodically driven quantum system Raditya Bomantara, Arne Grimsmo The Gottesman-Kitaev-Preskill (GKP) code is one of the most promising bosonic error correction codes, with good protection against natural noise and a relatively easy gate set. However, preparing high quality codewords is challenging. In this talk we present a relatively simple periodically driven quantum system whose Floquet eigenstates are approximate Gottesman-Kitaev-Preskill codewords. The system may be realized in a superconducting circuit consisting of an LC circuit shunted by a switchable Josephson junction. We show that high quality GKP codewords can be prepared, given a sufficiently fast on-off switching of the Josephson junction, and that environmental noise is highly suppressed in this regime. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S31.00009: Efficient simulatability of continuous-variable circuits with large Wigner negativity Laura García-Álvarez, Cameron Calcluth, Alessandro Ferraro, Giulia Ferrini Discriminating between quantum computing architectures that can provide quantum advantage from those that cannot is of crucial importance. Wigner negativity is known to be a necessary resource for computational advantage in several quantum-computing architectures, including those based on continuous variables. However, it is not a sufficient resource, and it is an open question under which conditions CV circuits displaying Wigner negativity offer the potential for quantum advantage. In this work, we identify vast families of circuits that display large Wigner negativity, and yet are classically efficiently simulatable, although they are not recognized as such by previously available theorems. These families of circuits employ bosonic codes based on either translational or rotational symmetries and can include both Gaussian and non-Gaussian gates and measurements. We derive our results by establishing a link between the simulatability of high-dimensional discrete-variable quantum circuits and bosonic codes. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S31.00010: Optimal tests for continuous-variable quantum teleportation and photodetectors Kunal Sharma, Barry Cyril Sanders, Mark Wilde Quantum teleportation is a primitive for several important applications, including quantum communication, quantum computation, error correction, and quantum networks. In this work, we propose an optimal test for the performance of continuous-variable (CV) quantum teleportation in terms of the energy-constrained channel fidelity between ideal CV teleportation and its experimental implementation. All work prior to ours considered suboptimal tests of the performance of CV teleportation, focusing instead on its performance for particular states, such as coherent states, squeezed states, cat states, etc. Here we prove that the optimal state for testing CV teleportation is an entangled superposition of twin-photon states. We establish this result by reducing the problem of estimating the energy-constrained minimum fidelity between ideal CV teleportation and its experimental approximation to a quadratic program and solving it. As an additional result, we obtain an analytical solution to the energy-constrained diamond distance between a photodetector and its experimental approximation. These results are relevant for experiments that make use of CV teleportation and photodetectors. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S31.00011: Propagating Wigner-negative states from the steady-state emission of a superconducting qubit Yong Lu, Ingrid Strandberg, Isaac Quijandria Diaz, Göran Johansson, Simone Gasparinetti, Per Delsing Nonclassical states of the electromagnetic field are an essential resource for quantum communication and quantum computation. Specifically, to obtain a quantum computational advantage it is necessary to have states that are nonclassical in the sense that they have a negative Wigner function. In circuit quantum electrodynamics setups, such nonclassical states have been generated in confined cavity modes. Propagating Wigner-negative states have been experimentally produced by either releasing a cavity state into a waveguide, or by pulsing a quantum system such as a qubit. Here, by contrast, we demonstrate the steady-state generation of propagating Wigner-negative states at steady state, from a continuously driven superconducting qubit. We reconstruct the Wigner function of the radiation emitted into various propagating modes, defined by their temporal envelopes, using linear amplifiers and digital filtering. We observe a large Wigner logarithmic negativity, in excess of 0.08, for an optimized temporal envelope, in agreement with theory. Our results provide an alternative route to engineer nonclassical states useful for quantum computation. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S31.00012: Efficient verification of continuous-variable quantum states and quantum devices beyond independent and identical assumption Yadong Wu, Bai Ge, Giulio Chiribella, Nana Liu Continuous-variable quantum information, where information is encoded in an infinite-dimensional Hilbert space, is widely used in many quantum information protocols including quantum computation, quantum metrology, quantum cryptography, etc. To demonstrate quantum advantage in these protocols, certification of realistic implementations of multimode continuous-variable quantum states and quantum devices is an essential step. However, in realistic scenarios, identical and independent (i.i.d) state preparation and calls to the quantum device cannot be generally guaranteed. Important instances include adversarial scenarios and instances of time-dependent and correlated noise. In this paper, we propose the first reliable schemes to verify multimode continuous-variable entangled states and devices in these non-i.i.d scenarios. |
Thursday, March 18, 2021 2:18PM - 2:30PM On Demand |
S31.00013: Complex two-mode quadratures - a generalized formalism for continuous-variable quantum optics Leon Bello, Yoad Michael, Michael Rosenbluh, Eliahu Cohen, Avi Pe'er Quantum squeezing, a major resource of quantum information processing and quantum metrology, is best analyzed in terms of the field quadratures – the quantum optical analogs of position and momentum, which form the continuous-variable formalism of quantum light. Degenerate squeezing admits a very neat and simple description in terms of the single-mode quadrature operators, but the non-degenerate case requires a more complicated treatment involving correlations between the quadratures of the different modes. |
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