1,721,004 research outputs found
On the classical capacity of quantum Gaussian channels
No full textThe set of quantum Gaussian channels acting on one bosonic mode can be classified according to the action of the group of Gaussian unitaries. We look for bounds on the classical capacity for channels belonging to such a classification. Lower bounds can be efficiently calculated by restricting to Gaussian encodings, for which we provide analytical expressions
Macroscopic entanglement by entanglement swapping
Get PDFWe present a scheme for entangling two micromechanical oscillators. The scheme exploits the quantum
effects of radiation pressure and it is based on a novel application of entanglement swapping, where
standard optical measurements are used to generate purely mechanical entanglement. The scheme is
presented by first solving the general problem of entanglement swapping between arbitrary bipartite
Gaussian states, for which simple input-output formulas are provided
Security of two-way quantum cryptography against asymmetric Gaussian attacks
No full textEditori: Meyers R. E., Shih Y., Deacon K. S
Capacities of linear quantum optical systems
No full textA wide variety of communication channels employ the quantized electromagnetic field to convey information. Their communication capacity crucially depends on losses associated to spatial characteristics of the channel such as diffraction and antenna design. Here we focus on the communication via a finite pupil, showing that diffraction is formally described as a memory channel. By exploiting this equivalence we then compute the communication capacity of an optical refocusing system, modeled as a converging lens. Even though loss of information originates from the finite pupil of the lens, we show that the presence of the refocusing system can substantially enhance the communication capacity. We mainly concentrate on communication of classical information, the extension to quantum information being straightforward
Quantum reading under a local energy constraint
No full textNonclassical states of light play a central role in many quantum information protocols. Very recently, their
quantum features have been exploited to improve the readout of information from digital memories, modeled as
arrays of microscopic beam splitters [Pirandola, Phys. Rev. Lett. 106, 090504 (2011)]. In this model of “quantum
reading,” a nonclassical source of light with Einstein-Podolski-Rosen correlations has been proven to retrieve
more information than any classical source. In particular, the quantum-classical comparison has been performed
under a global energy constraint, i.e., by fixing the mean total number of photons irradiated over each memory
cell. In this paper we provide an alternative analysis which is based on a local energy constraint, meaning that
we fix the mean number of photons per signal mode irradiated over the memory cell. Under this assumption,
we investigate the critical number of signal modes after which a nonclassical source of light is able to beat any
classical source irradiating the same number of signals
Mixed State Entanglement Classification using Artificial Neural Networks
Get PDFReliable methods for the classification and quantification of quantum entanglement are fundamental to understanding its exploitation in quantum technologies. One such method, known as Separable Neural Network Quantum States (SNNS), employs a neural network inspired parameterisation of quantum states whose entanglement properties are explicitly programmable. Combined with generative machine learning methods, this ansatz allows for the study of very specific forms of entanglement which can be used to infer/measure entanglement properties of target quantum states. In this work, we extend the use of SNNS to mixed, multipartite states, providing a versatile and efficient tool for the investigation of intricately entangled quantum systems. We illustrate the effectiveness of our method through a number of examples, such as the computation of novel tripartite entanglement measures, and the approximation of ultimate upper bounds for qudit channel capacities
Microwave quantum illumination using a digital receiver
Get PDFQuantum illumination is a powerful sensing technique that employs entangled signal-idler photon pairs to boost the detection efficiency of low-reflectivity objects in environments with bright thermal noise. The promised advantage over classical strategies is particularly evident at low signal powers, a feature which could make the protocol an ideal prototype for non-invasive biomedical scanning or low-power short-range radar. In this work we experimentally investigate the concept of quantum illumination at microwave frequencies. We generate entangled fields using a Josephson parametric converter to illuminate a room-temperature object at a distance of 1 meter in a free-space detection setup. We implement a digital phase conjugate receiver based on linear quadrature measurements that outperforms a symmetric classical noise radar in the same conditions despite the entanglement-breaking signal path. Starting from experimental data, we also simulate the case of perfect idler photon number detection, which results in a quantum advantage compared to the relative classical benchmark. Our results highlight the opportunities and challenges on the way towards a first room-temperature application of microwave quantum circuits
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