Error Probability Derivation in a Phonon-based Quantum Channel

International audienceQuantum communications are gaining more and more interest in the research community thanks to the recent advancements in nanotechnology. Indeed, quantum phenomena represent a natural direction for developing nanotechnology. The exploitation of quantum nature of information offers new potential solutions in the field of computing and networking, and extends the communication potentiality to levels that cannot be imagined in classical communication systems. Quantum communications can be realized in different ways. In this paper, we focus on the exploitation of quantum particles and quantum channels, in order to realize a data transmission system by means of phonons. First, we introduce the channel model of a phonon-based quantum system, and then derive the analysis of the error probability associated to such quantum channel. The application scenario is a biological environment, where phonons are exploited as information carriers. We have dealt a numerical evaluation in order to assess the performance of the quantum communication system. In particular, we have derived numerical results in terms of the error probability and the activity time, which represent how effective are phonons for communication purpose. We observe the frequency dependence of both error probability and activity time, thus allowing to tune the frequency for performance optimization

Interplay and optimization of decoherence mechanisms in the optical control of spin quantum bits implemented on a semiconductor quantum dot

We study the influence of the environment on an optically induced rotation of a single electron spin in a charged semiconductor quantum dot. We analyze the decoherence mechanisms resulting from the dynamical lattice response to the charge evolution induced in a trion-based optical spin control scheme. Moreover, we study the effect of the finite trion lifetime and of the imperfections of the unitary evolution such as off-resonant excitations and the nonadiabaticity of the driving. We calculate the total error of the operation on a spin-based qubit in an InAs/GaAs quantum dot system and discuss possible optimization against the different contributions. We indicate the parameters which allow for coherent control of the spin with a single qubit gate error as low as $10^{-4}$.Comment: Final version, 14 pages, 11 figure

Picosecond coherent electron motion in a silicon single-electron source

Understanding ultrafast coherent electron dynamics is necessary for application of a single-electron source to metrological standards, quantum information processing, including electron quantum optics, and quantum sensing. While the dynamics of an electron emitted from the source has been extensively studied, there is as yet no study of the dynamics inside the source. This is because the speed of the internal dynamics is typically higher than 100 GHz, beyond state-of-the-art experimental bandwidth. Here, we theoretically and experimentally demonstrate that the internal dynamics in a silicon singleelectron source comprising a dynamic quantum dot can be detected, utilising a resonant level with which the dynamics is read out as gate-dependent current oscillations. Our experimental observation and simulation with realistic parameters show that an electron wave packet spatially oscillates quantum-coherently at $\sim$ 200 GHz inside the source. Our results will lead to a protocol for detecting such fast dynamics in a cavity and offer a means of engineering electron wave packets. This could allow high-accuracy current sources, high-resolution and high-speed electromagnetic-field sensing, and high-fidelity initialisation of flying qubits

Shot Noise in Mesoscopic Conductors

Theoretical and experimental work concerned with dynamic fluctuations has developed into a very active and fascinating subfield of mesoscopic physics. We present a review of this development focusing on shot noise in small electric conductors. Shot noise is a consequence of the quantization of charge. It can be used to obtain information on a system which is not available through conductance measurements. In particular, shot noise experiments can determine the charge and statistics of the quasiparticles relevant for transport, and reveal information on the potential profile and internal energy scales of mesoscopic systems. Shot noise is generally more sensitive to the effects of electron-electron interactions than the average conductance. We present a discussion based on the conceptually transparent scattering approach and on the classical Langevin and Boltzmann-Langevin methods; in addition a discussion of results which cannot be obtained by these methods is provided. We conclude the review by pointing out a number of unsolved problems and an outlook on the likely future development of the field.Comment: 99 two-column pages; 38 .eps figures included. Submitted to Physics Reports. Many minor improvements; typos corrected; references added and update