Photon Counting Applications IV; and Quantum Optics and Quantum Information Transfer and Processing

Ivan Procházka, Roman Sobolewski, Miloslav Dušek

Ivan Procházka, Alan L. Migdall, A. Pauchard +3 more

Mark A. Itzler, S. Cova, Michael Wahl +1 more

The 21 papers in this special issue focus on single photon counting. The issue provides a survey of techniques employing photon counting in the study of biomolecular structure and function, and covers such applications as ranging and three-dimensional imaging and the exploitation of the photon's quantum mechanical properties in quantum optics and quantum information processing.

Junjie Liu, Hsing-Ta Chen, Dvira Segal

Quantum nondemolition (QND) measurements of photons is a much pursued endeavor in the field of quantum optics and quantum information processing. Here, we propose a hybrid optoelectromechanical platform that integrates a cavity system with a hybrid electromechanical probe for QND photon counting. Building upon a mechanical-mode-mediated nonperturbative electro-optical dispersive coupling, our protocol performs the QND photon counting measurement by means of the current-voltage characteristics of the probe. In particular, we show that the peak voltage shift of the differential conductance is linearly dependent on the photon occupation number, thus providing a sensitive measure of the photon number, especially in the strong optomechanical coupling regime. Given that our proposed hybrid system is compatible with state-of-the-art experimental techniques, we discuss its implementations and anticipate applications in quantum optics and polariton physics.

F. Daneshgaran, Maria Teresa Delgado, M. Mondin

This paper investigates the potential improvements that may be obtained in terms of the secret key transmission rate in a Quantum Key Distribution (QKD) scheme whereby photon-counting detectors are used at the receiver. To take full advantage of such detectors, soft information is generated in the form of Log-Likelihood Ratios (LLRs) using a Bayesian estimator of phase of the signal pulse which is used to carry the information. The technique is general in a sense that any optical communication scheme whereby the received mean photon count is relatively small, but not necessarily below one and uses the polarization state of light to transmit the binary data may benefit from the soft information processing proposed, although in this paper, we have focused on the QKD application. We demonstrate using simulations the significant reduction in the residual Bit Error Rate (BER) and Frame Error Rate (FER) that is achievable using the proposed soft information processing scheme for a given Quantum BER (QBER) on the quantum link, after the information reconciliation process using LDPC Forward Error Correction (FEC) coding.