Result

Robustness of topologically protected edge states in quantum walk experiments with neutral atoms

Date: 
2016-05-11
Author(s): 

Thorsten Groh, Stefan Brakhane, Wolfgang Alt, Dieter Meschede, Janos Asbóth, Andrea Alberti

Reference: 

arXiv:1605.03633 [quant-ph]

Discrete-time quantum walks allow Floquet topological insulator materials to be explored using controllable systems such as ultracold atoms in optical lattices. By numerical simulations, we study the robustness of topologically protected edge states in the presence of temporal disorder in one- and two-dimensional discrete-time quantum walks. We also develop a simple analytical model to gain further insight into the robustness of these edge states against either spin or spatial dephasing.

Super-resolution microscopy of single atoms in optical lattices

Date: 
2016-05-06
Author(s): 

Andrea Alberti, Carsten Robens, Wolfgang Alt, Stefan Brakhane, Michał Karski, René Reimann, Artur Widera and Dieter Meschede

Reference: 

New J. Phys. 18, 053010 (2016)

We report on image processing techniques and experimental procedures to determine the lattice-site positions of single atoms in an optical lattice with high reliability, even for limited acquisition time or optical resolution. Determining the positions of atoms beyond the diffraction limit relies on parametric deconvolution in close analogy to methods employed in super-resolution microscopy. We develop a deconvolution method that makes effective use of the prior knowledge of the optical transfer function, noise properties, and discreteness of the optical lattice.

A note on coherence power of N-dimensional unitary operators

Date: 
2015-10-22
Author(s): 

M. García-Díaz, D. Egloff, M.B. Plenio

Reference: 

arXiv:1510.06683

The coherence power of a quantum channel, that is, its ability to increase the coherence of input states, is a fundamental concept within the framework of the resource theory of coherence. In this note we discuss various possible definitions of coherence power. Then we prove that the coherence power of a unitary operator acting on a qubit, computed with respect to the l1-coherence measure, can be calculated by maximizing its coherence gain over pure incoherent states.

A measure of majorization emerging from single-shot statistical mechanics

Date: 
2015-07-02
Author(s): 

D. Egloff, O. C. O. Dahlsten, R. Renner, and V. Vedral

Reference: 

New J. Phys. 17 073001

The use of the von Neumann entropy in formulating the laws of thermodynamics has recently been challenged. It is associated with the average work whereas the work guaranteed to be extracted in any single run of an experiment is the more interesting quantity in general. We show that an expression that quantifies majorization determines the optimal guaranteed work. We argue it should therefore be the central quantity of statistical mechanics, rather than the von Neumann entropy.

Quantum metrology enhanced by repetitive quantum error correction

Date: 
2016-02-23
Author(s): 

Thomas Unden, Priya Balasubramanian, Daniel Louzon, Yuval Vinkler, Martin B. Plenio, Matthew Markham, Daniel Twitchen, Igor Lovchinsky, Alexander O. Sushkov, Mikhail D. Lukin, Alex Retzker, Boris Naydenov, Liam P. McGuinness, Fedor Jelezko

Reference: 

arXiv:1602.07144

The accumulation of quantum phase in response to a signal is the central mechanism of quantum sensing, as such, loss of phase information presents a fundamental limitation. For this reason approaches to extend quantum coherence in the presence of noise are actively being explored. Here we experimentally protect a room-temperature hybrid spin register against environmental decoherence by performing repeated quantum error correction whilst maintaining sensitivity to signal fields.

An Energy Based Scheme for Reconstruction of Piecewise Constant Signals observed in the Movement of Molecular Machines

Date: 
2015-04-29
Author(s): 

Joachim Rosskopf, Korbinian Paul-Yuan, Martin B. Plenio, Jens Michaelis

Reference: 

arXiv:1504.07873

Analyzing the physical and chemical properties of single DNA based molecular machines such as polymerases and helicases often necessitates to track stepping motion on the length scale of base pairs. Although high resolution instruments have been developed that are capable of reaching that limit, individual steps are oftentimes hidden by experimental noise which complicates data processing. Here, we present an effective two-step algorithm which detects steps in a high bandwidth signal by minimizing an energy based model (Energy based step-finder, EBS).

Ultrasensitive magnetometer using a single atom

Date: 
2014-11-28
Author(s): 

I. Baumgart, J.-M. Cai, A. Retzker, M. B. Plenio, Ch. Wunderlich

Reference: 

arXiv:1411.7893

Precision sensing, and in particular high precision magnetometry, is a central goal of research into quantum technologies. For magnetometers often trade-offs exist between sensitivity, spatial resolution, and frequency range. The precision, and thus the sensitivity of magnetometry scales as 1/(T2)1/2 with the phase coherence time, T2, of the sensing system playing the role of a key determinant.

Practical Entanglement Estimation for Spin-System Quantum Simulators

Date: 
2015-07-09 - 2016-03-09
Author(s): 

O. Marty, M. Cramer, and M. B. Plenio

Reference: 

Phys. Rev. Lett. 116, 105301

We present practical methods to measure entanglement for quantum simulators that can be realized with trapped ions, cold atoms, and superconducting qubits. Focusing on long- and short-range Ising-type Hamiltonians, we introduce schemes that are applicable under realistic experimental conditions including mixedness due to, e.g., noise or temperature. In particular, we identify a single observable whose expectation value serves as a lower bound to entanglement and that may be obtained by a simple quantum circuit.

Filter design for hybrid spin gates

Date: 
2015-04-21 - 2015-08-18
Author(s): 

Andreas Albrecht and Martin B. Plenio

Reference: 

Phys. Rev. A 92, 022340

The impact of control sequences on the environmental coupling of a quantum system can be described in terms of a filter. Here we analyze how the coherent evolution of two interacting spins subject to periodic control pulses, using the example of a nitrogen vacancy center coupled to a nuclear spin, can be described in the filter framework in both the weak- and the strong-coupling limit. A universal functional dependence around the filter resonances then allows for tuning the coupling type and strength.

Improved scaling of time-evolving block-decimation algorithm through reduced-rank randomized singular value decomposition

Date: 
2015-04-06 - 2015-06-15
Author(s): 

D. Tamascelli, R. Rosenbach, and M. B. Plenio

Reference: 

Phys. Rev. E 91, 063306

When the amount of entanglement in a quantum system is limited, the relevant dynamics of the system is restricted to a very small part of the state space. When restricted to this subspace the description of the system becomes efficient in the system size. A class of algorithms, exemplified by the time-evolving block-decimation (TEBD) algorithm, make use of this observation by selecting the relevant subspace through a decimation technique relying on the singular value decomposition (SVD). In these algorithms, the complexity of each time-evolution step is dominated by the SVD.

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