scholarly journals Universal and operational benchmarking of quantum memories

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Xiao Yuan ◽  
Yunchao Liu ◽  
Qi Zhao ◽  
Bartosz Regula ◽  
Jayne Thompson ◽  
...  
Keyword(s):  
Quantum Coherence ◽  
Quantum Memory ◽  
Statistical Sampling ◽  
Speed Up ◽  
Robustness To Noise ◽  
Non Local ◽  
Low Dimensional ◽  
Error Suppression

AbstractQuantum memory—the capacity to faithfully preserve quantum coherence and correlations—is essential for quantum-enhanced technology. There is thus a pressing need for operationally meaningful means to benchmark candidate memories across diverse physical platforms. Here we introduce a universal benchmark distinguished by its relevance across multiple key operational settings, exactly quantifying (1) the memory’s robustness to noise, (2) the number of noiseless qubits needed for its synthesis, (3) its potential to speed up statistical sampling tasks, and (4) performance advantage in non-local games beyond classical limits. The measure is analytically computable for low-dimensional systems and can be efficiently bounded in the experiment without tomography. We thus illustrate quantum memory as a meaningful resource, with our benchmark reflecting both its cost of creation and what it can accomplish. We demonstrate the benchmark on the five-qubit IBM Q hardware, and apply it to witness the efficacy of error-suppression techniques and quantify non-Markovian noise. We thus present an experimentally accessible, practically meaningful, and universally relevant quantifier of a memory’s capability to preserve quantum advantage.

scholarly journals Quantifying computational advantage of Grover’s algorithm with the trace speed

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Valentin Gebhart ◽  
Luca Pezzè ◽  
Augusto Smerzi
Keyword(s):  
Quantum Coherence ◽  
Search Algorithm ◽  
Quantum Algorithms ◽  
Physical Origin ◽  
Computational Advantage ◽  
Speed Up ◽  
Quantum Speed Up ◽  
Quantum Statistical ◽  
Grover’S Search Algorithm ◽  
General Physical

AbstractDespite intensive research, the physical origin of the speed-up offered by quantum algorithms remains mysterious. No general physical quantity, like, for instance, entanglement, can be singled out as the essential useful resource. Here we report a close connection between the trace speed and the quantum speed-up in Grover’s search algorithm implemented with pure and pseudo-pure states. For a noiseless algorithm, we find a one-to-one correspondence between the quantum speed-up and the polarization of the pseudo-pure state, which can be connected to a wide class of quantum statistical speeds. For time-dependent partial depolarization and for interrupted Grover searches, the speed-up is specifically bounded by the maximal trace speed that occurs during the algorithm operations. Our results quantify the quantum speed-up with a physical resource that is experimentally measurable and related to multipartite entanglement and quantum coherence.

scholarly journals Local and Non-Local Invasive Measurements on Two Quantum Spins Coupled via Nanomechanical Oscillations

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1078
Author(s):  
Dimitrios Maroulakos ◽  
Levan Chotorlishvili ◽  
Dominik Schulz ◽  
Jamal Berakdar
Keyword(s):  
Quantum Coherence ◽  
Indirect Measurement ◽  
Quantum Spin ◽  
Quantum States ◽  
Spin Interaction ◽  
First Case ◽  
Composite Quantum System ◽  
Local Quantum ◽  
Non Local ◽  
Quantum Spins

Symmetry plays the central role in the structure of quantum states of bipartite (or many-body) fermionic systems. Typically, symmetry leads to the phenomenon of quantum coherence and correlations (entanglement) inherent to quantum systems only. In the present work, we study the role of symmetry (i.e., quantum correlations) in invasive quantum measurements. We consider the influence of a direct or indirect measurement process on a composite quantum system. We derive explicit analytical expressions for the case of two quantum spins positioned on both sides of the quantum cantilever. The spins are coupled indirectly to each others via their interaction with a magnetic tip deposited on the cantilever. Two types of quantum witnesses can be considered, which quantify the invasiveness of a measurement on the systems’ quantum states: (i) A local quantum witness stands for the consequence on the quantum spin states of a measurement done on the cantilever, meaning we first perform a measurement on the cantilever, and subsequently a measurement on a spin. (ii) The non-local quantum witness signifies the response of one spin if a measurement is done on the other spin. In both cases the disturbance must involve the cantilever. However, in the first case, the spin-cantilever interaction is linear in the coupling constant Ω , where as in the second case, the spin-spin interaction is quadratic in Ω . For both cases, we find and discuss analytical results for the witness.

scholarly journals SLRL4D: Joint Restoration of Subspace Low-Rank Learning and Non-Local 4-D Transform Filtering for Hyperspectral Image

2020 ◽  
Vol 12 (18) ◽  
pp. 2979
Author(s):  
Le Sun ◽  
Chengxun He ◽  
Yuhui Zheng ◽  
Songze Tang
Keyword(s):  
Hyperspectral Image ◽  
Dimensional Subspace ◽  
Low Rank ◽  
Spatial Correlations ◽  
Self Similarity ◽  
Multiple Datasets ◽  
Alternating Direction ◽  
Non Local ◽  
Low Dimensional ◽  
Spatial Redundancy

During the process of signal sampling and digital imaging, hyperspectral images (HSI) inevitably suffer from the contamination of mixed noises. The fidelity and efficiency of subsequent applications are considerably reduced along with this degradation. Recently, as a formidable implement for image processing, low-rank regularization has been widely extended to the restoration of HSI. Meanwhile, further exploration of the non-local self-similarity of low-rank images are proven useful in exploiting the spatial redundancy of HSI. Better preservation of spatial-spectral features is achieved under both low-rank and non-local regularizations. However, existing methods generally regularize the original space of HSI, the exploration of the intrinsic properties in subspace, which leads to better denoising performance, is relatively rare. To address these challenges, a joint method of subspace low-rank learning and non-local 4-d transform filtering, named SLRL4D, is put forward for HSI restoration. Technically, the original HSI is projected into a low-dimensional subspace. Then, both spectral and spatial correlations are explored simultaneously by imposing low-rank learning and non-local 4-d transform filtering on the subspace. The alternating direction method of multipliers-based algorithm is designed to solve the formulated convex signal-noise isolation problem. Finally, experiments on multiple datasets are conducted to illustrate the accuracy and efficiency of SLRL4D.

scholarly journals QUANTUM EVOLUTION IN SPACE–TIME FOAM

1999 ◽  
Vol 14 (26) ◽  
pp. 4079-4120 ◽  
Author(s):  
LUIS J. GARAY
Keyword(s):  
Quantum Coherence ◽  
Planck Scale ◽  
Space Time ◽  
Low Energy ◽  
Quantum Evolution ◽  
Minimum Length ◽  
Resolution Limit ◽  
Large Length ◽  
Non Local ◽  
Quantum Mechanical Systems

In this work, I review some aspects concerning the evolution of quantum low-energy fields in a foamlike space–time, with involved topology at the Planck scale but with a smooth metric structure at large length scales, as follows. Quantum gravitational fluctuations may induce a minimum length thus introducing an additional source of uncertainty in physics. The existence of this resolution limit casts doubts on the metric structure of space–time at the Planck scale and opens a doorway to nontrivial topologies, which may dominate Planck scale physics. This foamlike structure of space–time may show up in low-energy physics through loss of quantum coherence and mode-dependent energy shifts, for instance, which might be observable. Space–time foam introduces non-local interactions that can be modeled by a quantum bath, and low-energy fields evolve according to a master equation that displays such effects. Similar laws are also obtained for quantum mechanical systems evolving according to good real clocks, although the underlying Hamiltonian structure in this case establishes serious differences among both scenarios.

scholarly journals Infrared generation in low-dimensional semiconductor heterostructures via quantum coherence

2001 ◽  
Vol 63 (5) ◽  
Author(s):  
A. A. Belyanin ◽  
F. Capasso ◽  
V. V. Kocharovsky ◽  
Vl. V. Kocharovsky ◽  
M. O. Scully
Keyword(s):  
Quantum Coherence ◽  
Semiconductor Heterostructures ◽  
Low Dimensional

scholarly journals Coherent modification of entanglement: benefits due to extended Hilbert space

2016 ◽  
Vol 16 (11&12) ◽  
pp. 954-968
Author(s):  
Dmitry Solenov
Keyword(s):  
Hilbert Space ◽  
Continuous Time ◽  
Computing System ◽  
Local Network ◽  
Toffoli Gate ◽  
Quantum Random Walks ◽  
Physical Systems ◽  
Time Quantum ◽  
Speed Up ◽  
Non Local

A quantum computing system is typically represented by a set of non-interacting (local) two-state systems—qubits. Many physical systems can naturally have more accessible states, both local and non-local. We show that the resulting non-local network of states connecting qubits can be efficiently addressed via continuous time quantum random walks, leading to substantial speed-up of multiqubit entanglement manipulations. We discuss a three-qubit Toffoli gate and a system of superconducting qubits as an illustration.

scholarly journals Analysis of Controlled Rabi Flopping in a Double Rephasing Photon Echo Scheme for Quantum Memories

Entropy ◽  
2020 ◽  
Vol 22 (9) ◽  
pp. 1007
Author(s):  
Rahmat Ullah ◽  
Byoung S. Ham
Keyword(s):  
Excited State ◽  
Phase Shift ◽  
Quantum Coherence ◽  
Photon Echo ◽  
Phase Control ◽  
Quantum Memory ◽  
Photon Echoes ◽  
Memory Applications

A double rephasing scheme of a photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of collective atom coherence. Unlike the rephasing-caused π-phase shift in a single rephasing scheme, the control Rabi flopping between the excited state and an auxiliary third state induces coherence inversion. Thus, the absorptive photon echo in a double rephasing scheme can be manipulated to be emissive. Here, we present a quantum coherence control of atom phases in a double rephasing photon echo scheme for emissive photon echoes for quantum memory applications.

scholarly journals Spatial patterns of glacier motion during a high-velocity event: Haut Glacier d’Arolla, Switzerland

2001 ◽  
Vol 47 (156) ◽  
pp. 9-20 ◽  
Author(s):  
Douglas Mair ◽  
Peter Nienow ◽  
Ian Willis ◽  
Martin Sharp
Keyword(s):  
Spatial Distribution ◽  
Horizontal Stress ◽  
Surface Strain ◽  
Strain Rates ◽  
Surface Motion ◽  
Local Forcing ◽  
Speed Up ◽  
Non Local ◽  
Glacier Motion ◽  
Resolution Data

AbstractThe surface motion of Haut Glacier d’Arolla, Switzerland, was monitored at a high spatial and temporal resolution. Data are analyzed to calculate surface velocities, surface strain rates and the components of the glacier force budget before, during and after an early melt season speed-up or “spring event”. We investigate the extent to which variations in glacier motion can be attributed to hydrologically induced local forcing or to non-local forcing transmitted via horizontal stress gradients. Enhanced glacier motion is dependent on a change in the spatial distribution of areas of high drag across the glacier.

scholarly journals Hidden Charge Orders in Low-Dimensional Mott Insulators

2019 ◽  
Vol 9 (4) ◽  
pp. 784
Author(s):  
Serena Fazzini ◽  
Arianna Montorsi
Keyword(s):  
Hubbard Model ◽  
Density Wave ◽  
Finite Size ◽  
Charge Order ◽  
Mott Insulators ◽  
Coulomb Interactions ◽  
Non Local ◽  
Low Dimensional ◽  
A Charge ◽  
Insulating Phase

The opening of a charge gap driven by interaction is a fingerprint of the transition to a Mott insulating phase. In strongly correlated low-dimensional quantum systems, it can be associated to the ordering of hidden non-local operators. For Fermionic 1D models, in the presence of spin–charge separation and short-ranged interaction, a bosonization analysis proves that such operators are the parity and/or string charge operators. In fact, a finite fractional non-local parity charge order is also capable of characterizing some two-dimensional Mott insulators, in both the Fermionic and the bosonic cases. When string charge order takes place in 1D, degenerate edge modes with fractional charge appear, peculiar of a topological insulator. In this article, we review the above framework, and we test it to investigate through density-matrix-renormalization-group (DMRG) numerical analysis the robustness of both hidden orders at half-filling in the 1D Fermionic Hubbard model extended with long range density-density interaction. The preliminary results obtained at finite size including several neighbors in the case of dipolar, screened and unscreened repulsive Coulomb interactions, confirm the phase diagram of the standard extended Hubbard model. Besides the trivial Mott phase, the bond ordered and charge density wave insulating phases are also not destroyed by longer ranged interaction, and still manifest hidden non-local orders.

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