Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S15: Quantum Networks and Open Systems |
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Sponsoring Units: DQI Chair: Emily Pritchett, HRL Labs Room: LACC 304C |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S15.00001: Interacting Photons in Curved Space Using Superconducting Circuits Mattias Fitzpatrick, Alicia Kollar, Andrew Houck After close to two decades of research and development, superconducting circuits have emerged as a rich platform for both quantum computation and quantum simulation. In this talk, we will discuss a new domain of quantum simulation with superconducting circuits: interacting photons in curved (non-Euclidean) space. By constructing two-dimensional lattices of microwave coplanar waveguide cavities with spatially-varying hopping rates and resonant frequencies, we demonstrate that we can simulate photons propagating in non-Euclidean space. Furthermore, superconducting circuits allow us to engineer effective photon-photon interactions using high kinetic inductance nonlinearites and transmon qubits--introducing the exciting prospect of studying strongly-interacting photons in curved geometries. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S15.00002: Open-System Quantum Error Correction Conditions Yink Loong Len, Hui Khoon Ng In this work, we present QEC conditions for a system undergoing open-system dynamics. Here, we describe the noise on the system as originating from a joint completely-positive, trace-preserving map on the system-bath composite, after which we trace out bath degrees of freedom. Our noise model can be viewed as an intermediate picture between the standard system-only quantum channel model and a system-bath Hamiltonian noise model: It goes beyond a Markovian description for the system dynamics, and yet retains a quantum dynamical semigroup structure for the problem. Our general noise model fits naturally into many physical scenarios where one has a relatively strong coupling between the system and an "intermediate" bath, which also couples weakly to a large dissipative bath. Despite the physical motivation from an intermediate bath, our noise model is mathematically general however, and in turn contains both system-only quantum channel model and system-bath Hamiltonian noise model as extreme cases. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S15.00003: Energy-Constrained Two-Way Assisted Private and Quantum Capacities of Quantum Channels Noah Davis, Maksim Shirokov, Mark Wilde With the rapid growth of quantum technologies, knowing the fundamental characteristics of quantum systems and protocols is essential to their effective implementation. The maximum rates at which a quantum channel can reliably transfer private and quantum information are respectively called the private and quantum capacities. Our contribution begins by formalizing the notion of energy-constrained private and quantum communication with the assistance of local operations and classical communication (LOCC). We then define the energy-constrained squashed entanglement of a channel and prove that it upper bounds the energy-constrained LOCC-assisted private and quantum capacities of an arbitrary channel with an arbitrary Hamiltonian when the channel and Hamiltonian are subject to certain physically well motivated conditions. We shift our focus to actual bosonic channels as an example of our general theory and prove that the two-mode squeezed vacuum optimizes the squashed entanglement for any single-mode phase-insensitive Gaussian channel whenever the squashing channel is constrained to be phase-insensitive and Gaussian. Finally, we extend the theory to the broadcast setting with one sender and multiple receivers. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S15.00004: Holographic Spin Networks from Tensor Network States Nathan McMahon, Sukhwinder Singh, Gavin Brennen Tensor networks are a powerful tool for describing many body systems, they reduce the complexity of storing and computing many-body states by restricting the state space to have a restricted entanglement structure. The multiscale entanglement renormalization ansatz (MERA) is one such example of tensor network state designed to approximate many body states with conformal symmetries (i.e. spin chains). For 1D periodic states the MERA can be visualized as a disc where the quantum state is on the boundary and the tensor network is embedded into the bulk of the disc, reminiscent of the holographic principle where theories of quantum gravity are expected to be encodable onto the system's boundary. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S15.00005: Measurement-based linear optics Rafael Alexander, Natasha Gabay, Peter Rohde, Nicolas Menicucci A major challenge in optical quantum processing is implementing large, stable interferometers. We offer a novel approach: virtual, measurement-based interferometers that are programed on the fly solely by the choice of homodyne measurement angles. The proposed continuous-variable cluster state architecture can be implemented on an unprecedented scale from compact experimental setups using either temporal or frequency modes. Our protocol minimizes noise due to finite squeezing. Furthermore, we show that this noise can be coaxed into appearing as pure photon loss per simulated optical element, where the efficiency of the interferometer is set by the overall squeezing parameter of the experiment. We compare our proposal to existing (physical) interferometers and consider its performance for BosonSampling, which could demonstrate postclassical computational power in the near future. We prove its efficiency in time and squeezing (energy) in this setting. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S15.00006: Efficiently controlling qubit networks Christian Arenz, Herschel Rabitz Future quantum devices often rely on favourable scaling with respect to the system components. To achieve desirable scaling, it is therefore crucial to implement unitary transformations in an efficient manner. We develop an upper bound for the minimum time required to implement a unitary transformation on a generic qubit network in which each of the qubits is subject to local time dependent controls. The set of gates is characterized that can be implemented in a time that scales at most polynomially in the number of qubits. Furthermore, we show how qubit systems can be concatenated through controllable two body interactions, making it possible to implement the gate set efficiently on the combined system. Finally a system is identified for which the gate set can be implemented with fewer controls. The considered model is particularly important, since it describes electron-nuclear spin interactions in NV centers. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S15.00007: Using Tikhonov Regularization Method to Solve the Hamiltonian in an Inverse Problem for a Quantum Spin System Ran Li Tikhonov regularization is a popular method for solving linear discrete ill-posed problems. This method can conveniently solve small-scale problems with the aid of the generalized singular value decomposition. However, it is impractical to use this decomposition for large-scale problems. We develop a new matrix decomposition method that are well suited for the solution of large-scale problems. This method can be applied to the inverse problem where we are given a set of desired orthogonal wave functions and we are trying to construct the parent Hamiltonian for a quantum spin system. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S15.00008: Improving Performance of an Analog Electronic Device Using Quantum Error Correction Corey Ostrove, Brian La Cour, S. Andrew Lanham, Granville Ott The development of the field of quantum information processing has resulted in countless techniques which exploit the properties of quantum mechanical systems in order to perform useful computational tasks. In this talk we discuss a particular application of protocols developed in the field quantum error correction (QEC) to a seemingly disparate field. The usefulness of analog classical systems for computation is generally thought to be complicated by the susceptibility of these devices to noise and the lack of a clear framework for achieving fault-tolerance. We present results for the application of quantum error correction techniques to a prototype analog computational device called a quantum emulation device (QED). It is shown that for the gates tested (Z, X and SH) there is a marked improvement in the performance characteristics. Gate performance after QEC, as measured by the average log-fidelity (-log_{10}(1-F)), increases by 2.15. This corresponds to a reduction in the infidelity of the gate operations by more than two orders of magnitude on average. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S15.00009: Finding decoherence-free subspaces numerically Purva Thakre, Mark Byrd For a particular subspace or subsystem, if the quantum information is preserved by a noise with exact symmetry then it is known as a decoherence free subspace or subsystem (DFS). A numerical method was proposed to identify such a DFS by Wang, Byrd and Jacobs (Phys. Rev. A 87, 012338 (2013)). An algebraic form that gives the structure of the DFS is decomposed into simple components and these components are then further decomposed into irreducible components. These irreducible components are then used to find a unitary transform that leaves the algebraic form invariant under such a transformation. We applied the same numerical method to find DFS's with more than 1 qubit. If a particular noise process is given then this numerical method could be used to find the subspace or subsystem that is not affected by the noise or is the least affected by the noise. The latter is known as a minimal-noise subspace or subsystem (MNS). |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S15.00010: Noise suppression via generalized-Markovian processes Jeffrey Marshall, Lorenzo Campos Venuti, Paolo Zanardi It is by now well established that noise itself can be useful for performing quantum information processing tasks. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S15.00011: Temperature Dependence of Spin Relaxation and Charge Noise in Silicon Spin Qubits Luca Petit, Jelmer Boter, GertJan Eenink, Gabriel Droulers, Marco Tagliaferri, Ruoyi Li, David Franke, Nicole Thomas, Jeanette Roberts, Ravi Pillarisetty, Payam Amin, Hubert C George, Kanwal Singh, James Clarke, Raymond Schouten, Slava Dobrovitski, Lieven Vandersypen, Menno Veldhorst Large-scale quantum computing is pursued by a wide variety of scientific disciplines. While leading solid-state approaches focus on decreasing the operation temperature to almost zero Kelvin, a crucial question is if the available cooling power will then be sufficient to increase the number of qubits to the required thousands or millions. |
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