Effect Of Local Noise Research Articles

Bell-inequality violation by dynamical Casimir photons in a superconducting microwave circuit

We study the Bell's inequality violation by dynamical Casimir radiation with pseudospin measurement. We consider a circuit quantum electrodynamical set-up where a relativistically moving mirror is simulated by variable external magnetic flux in a SQUID terminating a superconducting-microwave waveguide. We analytically obtain expectation values of the Bell operator optimized with respect to channel orientations, in terms of the system parameters. We consider the effects of local noise in the microwave field modes, asymmetry between the field modes resulting from nonzero detuning, and signal loss. Our analysis provides ranges of the above experimental parameters for which Bell violation can be observed. We show that Bell violation can be observed in this set-up up to 40 mK temperature as well as up to 65 % signal loss.

Entanglement sudden death: a threat to advanced quantum key distribution?

Entanglement is a global characteristic unique to quantum states that depends on quantum coherence and may allow one to carry out communications and information processing tasks that are either impossible or less efficient using classical states. Because environmental noise, even when entirely local in spatial extent, can fully destroy entanglement in finite time, an effect referred to as "entanglement sudden death" (ESD), it may threaten quantum information processing tasks. Although it may be possible to "distill" entanglement from a collection of noise-affected systems under appropriate circumstances, once entanglement has been completely lost no amount of distillation can recover it. It is therefore extremely important to avoid its complete destruction in times comparable to those of information processing tasks. Here, the effect of local noise on a class of entangled states used in entanglement-based quantum key distribution is considered and the threat ESD might pose to it is assessed.

Spatially resolved single photon detection with a quantum sensor array

We propose a method of resolving a spatially coherent signal, which contains on average just a single photon, against the background of local noise at the same frequency. The method is based on detecting the signal simultaneously in several points more than a wavelength apart through the entangling interaction of the incoming photon with the quantum metamaterial sensor array. The interaction produces the spatially correlated quantum state of the sensor array, characterised by a collective observable (e.g., total magnetic moment), which is read out using a quantum nondemolition measurement. We show that the effects of local noise (e.g., fluctuations affecting the elements of the array) are suppressed relative to the signal from the spatially coherent field of the incoming photon as , where N is the number of array elements. The realisation of this approach in the microwave range would be especially useful and is within the reach of current experimental techniques.

Correlation Detection in Local-Noise Fields

This paper is concerned with the effect of local noise on the ability of a correlation system to detect a distant, localized signal source. Each of two receiving points is surrounded by a local, circular noise field. Additional noise is assumed to arise from a circular field of infinite radius. The mean and variance of the detector output are computed and the output signal-to-noise ratio is determined. The degradations in signal-to-noise ratio resulting from local noise and also from finite receiving-point spacing are examined in detail when the local noise crosscorrelation is taken to be negligible. Finally, the local-noise crosscorrelation is investigated. Upper bounds are found, the maximum correlation over steering delay is examined, and the delay locations of maximum correlation are determined.