Non-Gaussian continuous-variable quantum states represent a pivotal resource in many quantum information protocols. Production of such states can occur through photonic subtraction process either at the transmitter side prior to sending a state through the channel, or at the receiver side on receipt of a state that has traversed the channel. In the context of quantum protocols implemented over communication channels to and from Low-Earth-Orbit (LEO) satellites it is unclear what photonic subtraction set-up will provide for the best performance. In this work we show that for a popular version of continuous-variable Quantum Key Distribution between terrestrial stations and LEO satellites, photon subtraction at the transmitter side is the preferred set-up. Such a result is opposite to that found for fiber-based implementations. Our results have implications for all future space-based missions that seek to take advantage of the opportunities offered by non-Gaussian quantum states.

We propose a time-correlated Markovian quantum channel (TCMQC) with an arbitrary degree of channel memory. This quantum channel accounts for spontaneous emission, pumping, and virtual processes, and can explain the dynamics of quantum correlation between two consecutive uses of a quantum channel. We obtain a Kraus representation of the stochastic map of TCMQCs by solving a Lindbladian master equation with eigenoperator variants. The derived stochastic dynamic map encompasses well-known Markovian quantum channels such as phase damping channels, amplitude damping channels, and thermal field channels with an arbitrary degree of channel memory. We then investigate the dynamics of the quantum entanglement affected by the influence of TCMQCs in terms of channel decoherence parameters such as the equilibrium state of atomic inversion and decay rates.

The performance of free-space optical quantum communications deteriorates due to the presence of atmosphere turbulence. In this paper, the $P$-function of a coherent state passing through a turbulent atmosphere channel in the presence of thermal noise is derived using the additive property of the thermal noise channel. The analytical form of the density operator for this turbulent coherent state and its corresponding matrix representation in Fock basis is deducted. Using this matrix representation of density operator for turbulent coherent state, the error probability of optical quantum communication system for binary phase shift keying is analyzed.

Quantum 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.

Faithful transmission of quantum information over noisy channel is an essential requisite for quantum communication and distributed quantum computing. Here we experimentally demonstrate a noise-rejecting scheme for single-photon qubits transmission, resorting to neither ancillary photons nor globally entangled resources. Employing the unbalanced polarization interferometer, the polarization qubits are transformed to time-bin degrees of freedom. Meanwhile, the deterministic transmission of quantum states with high fidelity can be achieved. We find that the immunity of time-bin encoded qubits against collective noise paves the way to practical quantum error- correction and rejection in long-distance quantum communication.

Cyberculture of quantum memory-driven computing integrates emerging technologies of parallel solution for time-consuming combinatorial problems. A scalable map of research relevant to quantum cyberculture is aimed at creating parallel algorithms for SoC Design and Test. The memory-driven innovation architecture of quantum computing is presented, which is defined by the leverage of photon read-write transactions on the structure of electrons in the absence of logic, associated with superposition and entanglement. A class of logical X-functions and their qubit models is introduced, that are technologically feasible for test, diagnosis, and fault simulation of SoC components. The architecture of services for design, test and verification of digital devices based on qubit models of logical primitives is described. A service for fault-free circuits simulation based on the qubit coverage of functional primitives is given. The models, cubit data structures and methods are focused and simulated on the classical computers by leveraging unitary coding binary states.

We introduce a generalization of quantum walks with entangled coins consisting of a model of discrete quantum walks with coin pairs under various degrees of entanglement and walkers in quantum superposition as initial states. We introduce novel position probability distributions that may be used for algorithm development based on quantum-mechanical phenomena. Also, we numerically show that the skewness of position probability distribution produced by using coin initial state with various degrees of entanglement cannot be easily inferred.

Backscattered signals are always obscured by the unavoidable channel noise. However, by exploiting quantum physics recent protocols had been developed to enhance the probability of detecting backscattered signals in a very noisy environment\cite{jantti2017multiantenna, di2018quantum}. In this paper we propose a new detection scheme that is simpler in nature than the sum frequency receiver that was proposed in the quantum illumination protocol\cite{zhuang2017optimum}. Signals are generated using spontaneous parametric down conversion (SPDC) and will be transmitted via the simple modulation technique of on-off keying (OOK), while the receiver design will rely upon the purely non-classical Hong-Ou-Mandel (HOM) effect.

We develop a non-cooperative game-theoretic model for the problem of graph minor-embedding to show that optimal compiling of adiabatic quantum programs in the sense of Nash equilibrium is possible.

Stabilizer codes over qudits have been widely studied but their encoding procedures have not been investigated in detail by many. The encoding procedure proposed previously by Grassl et al. generates the stabilizer codes over qudits for prime (d), while it may only generate a subspace of the codespace over qudits where (d) is a power of a prime. In this paper, we propose an encoding procedure to generate the stabilizer codes over qudits for (d) being a power of a prime. The procedure involves reducing the problem of encoding over qudits with (d={p}^{k}) to a problem similar to encoding over qudits with (d=p).

Quantum key distribution (QKD) protocols are designed to distribute secure keys between two remote parties. Current QKD systems require the presence of a trusted relay to distribute the keys over intercontinental distances, due to technological limitations. When the trusted relay is intermittently available to the end parties, as in the case of low Earth orbit (LEO) satellites, the QKD system undergoes a severe reduction in the amount of exchangeable secret bits. This paper proposes a new way to analyze the performance of QKD systems under these premises. It is shown that the secret key rate is not the most important figure of merit in the design of QKD protocols with intermittent relays, despite its importance for standard QKD links.

Inter-symbol-interference (ISI) noise in Continuous Variable Quantum Key Distribution (CVQKD) is caused by the overlap between the consecutive detected signals. In practice, this problem limits the repetition rate of the quantum signals for a given bandwidth detector and hence reduces the rate of secure key generation. We propose a method of using equalization to mitigate ISI noise in CVQKD systems. Its feasibility is studied using an analytical model with practical parameters. The improved performance of CVQKD detection is investigated using secure key analysis. The simulation results show an increase of 12.8 Mbits/s in secure key rate for a 1GHz bandwidth CVQKD system operating over a 20 km link.

The highly-excited Rydberg states are with a unique property of radio-frequency (RF) resonance, and Rydberg atoms at room temperature are promising for developing broadband RF electric field sensor and relevant metrology standard. In this paper, the working mechanism of an atomic amplitude modulation(AM) radio receiver is investigated in detail, the modulation RF signal can be directly retrieved by measuring the transmission of a probe laser at resonance of rubidium D2 transition using a fast photo-diode detector, without any conventional demodulation process. Various communication experiments are tested at a 10.22 GHz carrier, and a modulation bandwidth of ~MHz and an acceptable data transfer rate of ~Mbps have been achieved using current detection techniques. Owing to a potential high sensitivity and ultra-broadband capability of free-space RF field sensing, the quantum receiver has great significance compared with conventional electronics-based receivers, including but not limited to weak signal, long-distance and broadband communication in free space or via a fiber-link.

The finite-key effects in quantum access networks are studied. We consider a quantum-classical network where each user is equipped with a certain wavelength to exchange secure keys, using quantum key distribution techniques, and another one to exchange classical data. Users are connected to the central office via a passive optical network. The quantum users are connected to the fiber links via an indoor wireless channel. We investigate the regimes of operation within which a secure key can be exchanged in a reasonable amount of time. We find out that by properly designing the system, it is possible to run both quantum and classical systems at their full capacity.

The extensive studies on the quantum communication, which provides a novel means of secure communication, have been carried out in last decades. Among the various types of quantum communication, quantum secure direct communication (QSDC) can securely transmit message directly through a quantum channel. This paper reports a practical scheme of QSDC without quantum memory, taking advantage of the wiretap channel theory and classical coding theory. The proposed approach solves one of the biggest obstacle of practical applications of QSDC, the quantum memory, which is indispensable in original QSDC protocols. The design and detailed scheme for implementation of the proposed protocol are given.

The compression of geometry data is an important aspect of bandwidth-efficient data transfer for distributed 3d computer vision applications. We propose a quantum-enabled 3d point cloud lossy compression pipeline based on the Constructive Solid Geometry (CSG) model representation. Key parts of the pipeline are mapped to problems that are in NP for which an efficient ising formulation suitable for the execution on a Quantum Annealer exists. We describe existing ising formulations for the maximum clique search problem and the smallest exact cover problem, both of which are important building blocks of the proposed compression pipeline. Additionally, we discuss the properties of the overall pipeline regarding result optimality and described ising formulations.