QIPC

Shortcut to Adiabaticity in the Lipkin-Meshkov-Glick Model

Date: 
2015-05-01
Author(s): 

Steve Campbell, Gabriele De Chiara, Mauro Paternostro, G. Massimo Palma, and Rosario Fazio

Reference: 

Phys. Rev. Lett. 114, 177206 (2015)

We study transitionless quantum driving in an infinite-range many-body system described by the Lipkin-Meshkov-Glick model. Despite the correlation length being always infinite the closing of the gap at the critical point makes the driving Hamiltonian of increasing complexity also in this case. To this aim we develop a hybrid strategy combining a shortcut to adiabaticity and optimal control that allows us to achieve remarkably good performance in suppressing the defect production across the phase transition.

Hologram of a Single Photon

Date: 
2016-01-11
Author(s): 

Radosław Chrapkiewicz, Michał Jachura, Konrad Banaszek, Wojciech Wasilewski

The spatial structure of single photons is becoming an extensively explored resource used for facilitating the free-space quantum key distribution and quantum computation as well as for benchmarking the limits of quantum entanglement generation with orbital angular momentum modes or reduction of the photon free-space propagation speed.

Super-additivity in communication of classical information through quantum channels from a quantum parameter estimation perspective

Date: 
2016-03-01
Author(s): 

Jan Czajkowski, Marcin Jarzyna, Rafał Demkowicz-Dobrzański

We point out a contrasting role the entanglement plays in communication and estimation scenarios.
In the first case it brings noticeable benefits at the measurement stage (output super-additvity),
whereas in the latter it is the entanglement of the input probes that enables significant performance
enhancement (input super-additvity). We identify a weak estimation regime where a strong connection
between concepts crucial to the two fields is demonstrated; the accessible information and the
Holevo quantity on one side and the quantum Fisher information related quantities on the other.

Scheme for on-chip verification of transverse mode entanglement using the electro-optic effect

Date: 
2015-12-28
Author(s): 

Divya Bharadwaj, K. Thyagarajan, Michał Jachura, Michał Karpiński, Konrad Banaszek

Reference: 

Optics Express 23, 33087-33098 (2015) http://arxiv.org/pdf/1510.04204v2.pdf

A key ingredient in emerging quantum-enhanced technologies is the ability to coherently manipulate and detect superpositions of basis states. In integrated optics implementations, transverse spatial modes supported by multimode structures offer an attractive carrier of quantum superpositions. Here we propose an integrated dynamic mode converter based on the electro-optic effect in nonlinear channel waveguides for deterministic transformations between mutually non-orthogonal bases of spatial modes.

Phase noise in collective binary phase shift keying with Hadamard words

Date: 
2016-05-10
Author(s): 

Marcin Jarzyna, Victoria Lipińska, Aleksandra Klimek, Konrad Banaszek, Matteo G. A. Paris

Reference: 

Optics Express 24, 1693-1698 (2016) https://arxiv.org/abs/1509.00009

We analyze the effect of phase fluctuations in an optical communication scheme based on collective detection of sequences of binary coherent state symbols using linear optics and photon counting. When the phase noise is absent, the scheme offers qualitatively improved nonlinear scaling of the spectral efficiency with the mean photon number in the low-power regime compared to individual detection.

Mode engineering for realistic quantum-enhanced interferometry

Date: 
2016-04-29
Author(s): 

Michał Jachura, Radosław Chrapkiewicz, Rafał Demkowicz-Dobrzański, Wojciech Wasilewski, Konrad Banaszek

Reference: 

Nature Communications 7, 11411 (2016) http://arxiv.org/pdf/1504.05435.pdf

Quantum metrology overcomes standard precision limits by exploiting collective quantum superpositions of physical systems used for sensing, with the prominent example of non-classical multiphoton states improving interferometric techniques. Practical quantum-enhanced interferometry is, however, vulnerable to imperfections such as partial distinguishability of interfering photons. Here we introduce a method where appropriate design of the modal structure of input photons can alleviate deleterious effects caused by another, experimentally inaccessible degree of freedom.

The ultimate precision limits for noisy frequency estimation

Date: 
2016-03-24
Author(s): 

Andrea Smirne, Jan Kołodyński, Susana F. Huelga, Rafał Demkowicz-Dobrzański

Reference: 

Phys. Rev. Lett. 116, 120801 (2015) http://arxiv.org/pdf/1511.02708.pdf

Quantum metrology protocols allow us to surpass precision limits typical to classical statistics. However, in recent years, no-go theorems have been formulated, which state that typical forms of uncorrelated noise can constrain the quantum enhancement to a constant factor and, thus, bound the error to the standard asymptotic scaling. In particular, that is the case of time-homogeneous (Lindbladian) dephasing and, more generally, all semigroup dynamics that include phase covariant terms, which commute with the system Hamiltonian.

Nonclassicality of Temporal Correlations

Date: 
2015-09-18
Author(s): 

Stephen Brierley, Adrian Kosowski, Marcin Markiewicz, Tomasz Paterek, Anna Przysiężna

Reference: 

Phys. Rev. Lett. 115, 120404 (2015) http://arxiv.org/abs/1501.03505

The results of spacelike separated measurements are independent of distant measurement settings, a property one might call two-way no-signaling. In contrast, timelike separated measurements are only one-way no-signaling since the past is independent of the future but not vice versa. For this reason some temporal correlations that are formally identical to nonclassical spatial correlations can still be modeled classically.

Quantum interferometric measurements of temperature

Date: 
2015-09-10
Author(s): 

Marcin Jarzyna, Marcin Zwierz

Reference: 

Phys. Rev. A 92, 032112 (2015) http://arxiv.org/abs/1412.5609

We provide a detailed description of the quantum interferometric thermometer, which is a device that estimates the temperature of a sample from the measurements of the optical phase.

Improved Quantum Magnetometry beyond the Standard Quantum Limit

Date: 
2015-07-22
Author(s): 

J. B. Brask, R. Chaves, J. Kołodyński

Reference: 

Phys. Rev. X 5, 031010 (2015) http://arxiv.org/abs/1411.0716

Under ideal conditions, quantum metrology promises a precision gain over classical techniques scaling quadratically with the number of probe particles. At the same time, no-go results have shown that generic, uncorrelated noise limits the quantum advantage to a constant factor.

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