Transmission Of Classical Information Research Articles

Cryptography with stochastic photons

Quantum cryptography protocols are based on the use of quantum objects with at least two orthogonal states, for example, the polarization states of a photon. We propose a completely different cryptography protocol using a stochastic flow of single photons. Our method is based on the stochastic decay of an ensemble of radioactive nuclei randomly emitting a stream of γ-photons. We have experimentally demonstrated the transmission of classical information containing binary bits. Reading this information requires precise knowledge of the repetition rate of its sending. Otherwise, it is impossible to make the transmitted information visible, since it will be lost in the noise.

Optical mode conversion via spatiotemporally modulated atomic susceptibility.

Light is an excellent medium for both classical and quantum information transmission due to its speed, manipulability, and abundant degrees of freedom into which to encode information. Recently, space-division multiplexing has gained attention as a means to substantially increase the rate of information transfer by utilizing sets of infinite-dimensional propagation eigenmodes such as the Laguerre-Gaussian "donut" modes. Encoding in these high-dimensional spaces necessitates devices capable of manipulating photonic degrees of freedom with high efficiency. In this work, we demonstrate controlling the optical susceptibility of an atomic sample can be used as powerful tool for manipulating the degrees of freedom of light that pass through the sample. Utilizing this tool, we demonstrate photonic mode conversion between two Laguerre-Gaussian modes of a twisted optical cavity with high efficiency. We spatiotemporally modulate the optical susceptibility of an atomic sample that sits at the cavity waist using an auxiliary Stark-shifting beam, in effect creating a mode-coupling optic that converts modes of orbital angular momentum l = 3 → l = 0. The internal conversion efficiency saturates near unity as a function of the atom number and modulation beam intensity, finding application in topological few-body state preparation, quantum communication, and potential development as a flexible tabletop device.

Channel capacity of relativistic quantum communication with rapid interaction

In this work we study nonperturbatively the transmission of classical and quantum information in globally hyperbolic spacetimes, where the communication channel is between two qubit detectors interacting with a quantized massless scalar field via delta-coupling interaction. This interaction approximates very rapid detector-field interaction, effectively occurring at a single instant in time for each detector. We show that when both detectors interact via delta-coupling, one can arrange and tune the detectors so that the channel capacity is (at least) as good as the quantum channel constructed nonperturbatively using \textit{gapless detectors} by Landulfo [PRD 93, 104019]. Furthermore, we prove that this channel capacity is in fact optimal, i.e., both nonperturbative methods give essentially the same channel capacity, thus there is a sense in which the two methods can be regarded as equivalent as far as relativistic quantum communication is concerned.

Protected Quantum Teleportation Through Noisy Channel by Weak Measurement and Environment-Assisted Measurement

Quantum teleportation as a key protocol for quantum communication and quantum computing demonstrates the stark difference between quantum and classical information transmission. An ideal teleportation protocol requires pure maximally entangled state as the teleportation channel, while in real implementations the shared entanglement is severely degraded due to decoherence. In this letter, we propose a scheme to protect the quantum teleportation from decoherence by means of environment assisted measurement with weak measurements and flip operations. We show that the teleportation fidelity of our proposed scheme is significantly improved compared to teleportation with no protection and a teleportation protocol based on quantum measurement reversal. Also, the explicit formula of average teleportation fidelity and success probability of the entanglement protection are derived.

Classical state masking over a quantum channel

Transmission of classical information over a quantum state-dependent channel is considered, when the encoder can measure channel side information (CSI) and is required to mask information on the quantum channel state from the decoder. In this quantum setting, it is essential to conceal the CSI measurement as well. A regularized formula is derived for the masking equivocation region, and a full characterization is established for a class of measurement channels.

Capacities of Gaussian Quantum Channels With Passive Environment Assistance

Passive environment assisted communication takes place via a quantum channel modeled as a unitary interaction between the information carrying system and an environment, where the latter is controlled by a passive helper, who can set its initial state such as to assist sender and receiver, but not help actively by adjusting her behaviour depending on the message. Here we investigate the information transmission capabilities in this framework by considering Gaussian unitaries acting on Bosonic systems. We consider both quantum communication and classical communication with helper, as well as classical communication with free classical coordination between sender and helper (conferencing encoders). Concerning quantum communication, we prove general coding theorems with and without energy constraints, yielding multi-letter (regularized) expressions. In the search for cases where the capacity formula is computable, we look for Gaussian unitaries that are universally degradable or anti-degradable. However, we show that no Gaussian unitary yields either a degradable or anti-degradable channel for all environment states. On the other hand, restricting to Gaussian environment states, results in universally degradable unitaries, for which we thus can give single-letter quantum capacity formulas. Concerning classical communication, we prove a general coding theorem for the classical capacity under and energy constraint, given by a multi-letter expression. Furthermore, we derive an uncertainty-type relation between the classical capacities of the sender and the helper, helped respectively by the other party, showing a lower bound on the sum of the two capacities. Then, this is used to lower bound the classical information transmission rate in the scenario of classical communication between sender and helper.

Single-Shot Secure Quantum Network Coding for General Multiple Unicast Network With Free One-Way Public Communication

It is natural in a quantum network system that multiple users intend to send their quantum message to their respective receivers, which is called a multiple unicast quantum network. We propose a canonical method to derive a secure quantum network code over a multiple unicast quantum network from a secure classical network code. Our code correctly transmits quantum states when there is no attack. It also guarantees the secrecy of the transmitted quantum state even with the existence of an attack when the attack satisfies a certain natural condition. In our security proof, the eavesdropper is allowed to modify wiretapped information dependently on the previously wiretapped messages. Our protocol guarantees the secrecy by utilizing one-way classical information transmission (public communication) in the same direction as the quantum network although the verification of quantum information transmission requires two-way classical communication. In the protocol, some nodes may share secret randomness as resources in advance. Our secure network code can be applied to several networks including the butterfly network.

Entanglement-Assisted Communication Surpassing the Ultimate Classical Capacity.

Entanglement underpins a variety of quantum-enhanced communication, sensing, and computing capabilities. Entanglement-assisted communication (EACOMM) leverages entanglement preshared by communicating parties to boost the rate of classical information transmission. Pioneering theory works showed that EACOMM can enable a communication rate well beyond the ultimate classical capacity of optical communications, but an experimental demonstration of any EACOMM advantage remains elusive. In this Letter we report the implementation of EACOMM surpassing the classical capacity over lossy and noisy bosonic channels. We construct a high-efficiency entanglement source and a phase-conjugate quantum receiver to reap the benefit of preshared entanglement, despite entanglement being broken by channel loss and noise. We show that EACOMM beats the Holevo-Schumacher-Westmoreland capacity of classical communication by up to 16.3%, when both protocols are subject to the same power constraint at the transmitter. As a practical performance benchmark, we implement a classical communication protocol with the identical characteristics for the encoded signal, showing that EACOMM can reduce the bit-error rate by up to 69% over the same bosonic channel. Our work opens a route to provable quantum advantages in a wide range of quantum information processing tasks.

A Motor Rehabilitation BMI System Design Through Improving the SJIT Model and Introducing an MPC-based Auxiliary Controller

In the brain-machine interface (BMI) system, improving the motor recovery function of the joint and enabling the joint to adequately track the target trajectory are our main concerns. In this paper, to further improve the motor recovery effectiveness, two tasks are completed. First, a classical single-joint information transmission (SJIT) model is analyzed and improved by introducing several neurons. Second, an auxiliary controller that provides control inputs to the cerebral cortex is designed based on the model predictive control (MPC) strategy and is used to formulate a closed-loop motor rehabilitation BMI system based on the improved model. The simulation results show that the improved model can more accurately track the target movement trajectory than the SJIT model, and the designed BMI system can adequately recover the motor function of the joint. The sum of squared error (SSE) between the desired joint position trajectory and the output joint position trajectory is only $$1.2842 \times 10^{-5}$$ . In addition, under noises and disturbances, the BMI system can well recover the motor function of the joint. The model improvement and the designed BMI system are both effective.

Strong Converse Bounds in Quantum Network Information Theory

In this paper, we develop the first method for finding strong converse bounds in quantum network information theory. The general scheme relies on a recently obtained result in the field of non-commutative functional inequalities, namely the tensorization property of quantum reverse hypercontractivity for the quantum depolarizing semigroup. We develop a novel technique to employ this result to find both finite blocklength and exponential strong converse bounds for the tasks of quantum source coding with compressed classical side information, and distributed quantum hypothesis testing with communication constraints for a classical-quantum state. In the classical setting, these two problems can be reformulated in a unified framework in terms of the so-called image-size characterization problem, which we extend to the classical-quantum setting. We also use this technique to establish analogous strong converse bounds in broadcast communication scenarios. In particular, we consider the transmission of classical information through a degraded broadcast channel, whose outputs are two quantum systems, with the state of one being a degraded version of the other. In establishing this last result, we prove a second-order Fano-type inequality, which is of independent interest. Our method to study strong converses has potential applications in other important tasks of quantum network information theory.

Quantum-Enabled Communication without a Phase Reference.

A phase reference has been a standard requirement in continuous-variable quantum sensing and communication protocols. However, maintaining a phase reference is challenging due to environmental fluctuations, preventing quantum phenomena such as entanglement and coherence from being utilized in many scenarios. We show that quantum communication and entanglement-assisted communication without a phase reference are possible, when a short-time memory effect is present. The degradation in the communication rate of classical or quantum information transmission decreases inversely with the correlation time. Exact solutions of the quantum capacity and entanglement-assisted classical and quantum capacity for pure dephasing channels are derived, where non-Gaussian multipartite-entangled states show strict advantages over usual Gaussian sources. For thermal-loss dephasing channels, lower bounds of the capacities are derived. The lower bounds also extend to scenarios with fading effects in the channel. In addition, for entanglement-assisted communication, the lower bounds can be achieved by a simple phase-encoding scheme on two-mode squeezed vacuum sources, when the noise is large.

Microwave controlled ground state coherence in an atom-based optical amplifier

We experimentally investigate and theoretically analyze the effect of microwave controlled atomic ground state coherence on the phase-dependent amplification (PDA) of an optical probe field. We use three hyperfine levels in room temperature 85Rb atoms, which are cyclically connected by two optical and one microwave electromagnetic field. We show that a simultaneous fulfilment of a two-photon resonance condition that creates ground state coherence and a three-photon resonance condition leads to a significantly higher amplification of 7.5 dB of the optical probe field with a visibility of 98.8 %. By selectively breaking the ground state coherence using microwaves, we show that the amplification reduces with a bandwidth of 5 MHz. Nevertheless, the system shows non-zero PDA for large two-photon detunings of 15 MHz with high visibility of 66.8 %. This novel, controllable hybrid-PDA can be potentially used to trade-off amplification for bandwidth during the transmission of phase coherent classical and quantum information.

Single-Serving Quantum Broadcast Channel With Common, Individualized, and Confidential Messages

The two-receiver broadcast channel with primary and third party receivers is studied. The sender wishes to reliably communicate a common (or public) message to both receivers as well as individualized and confidential messages to the primary receiver only. The third party receiver must be kept completely ignorant of the confidential message but there are no secrecy requirements associated to the individualized message. A trade-off arises between the rates of the three messages: when one of the rates is high, the other rates may need to back off to guarantee the reliable transmission of all three messages. In addition, the confidentiality requirement implies availability of local randomness at the transmitter in order to implement a stochastic encoding. This article studies the trade-off between the rates of the common, individualized and confidential messages as well as that of the local randomness in the one-shot regime of a quantum broadcast channel. We provide an achievability region, by proving a conditional version of the convex-split lemma combined with the position-based decoding, as well as a (weak) converse region. We study the asymptotic behaviour of our bounds and recover several well-known asymptotic results in the literature, including simultaneous transmission of classical and quantum information.

Hierarchical simultaneous entanglement swapping for multi-hop quantum communication based on multi-particle entangled states* *Project supported by the National Natural Science Foundation of China (Grant No. 61971348), the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 16JK1711), and the Natural Science Foundation Research Project of Shaanxi Province, China (Grant No. 2016JQ6033).

Entanglement swapping is a key technology for multi-hop communication based on entanglement in quantum networks. However, the end-to-end delay of the traditional sequential entanglement swapping (SEQES) grows rapidly with the increase of network scale. To solve this problem, we first propose a low-delay multi-particle simultaneous entanglement swapping (SES) scheme to establish the remote four-particle Greenberger–Horne–Zeilinger (GHZ) channel states for the bidirectional teleportation of three-particle GHZ states, in which the intermediate nodes perform Bell state measurements, send the measurement results and the Bell state type to the user node Bob (or Alice) through classical channel simultaneously. Bob (or Alice) only needs to carry out a proper unitary operation according to the information he (or she) has received. Further, we put forward a hierarchical simultaneous entanglement swapping (HSES) scheme to reduce the classical information transmission cost, which is composed of level-1 SES and level-2 SES (schemes). The former is an inner segment SES, and the latter is an inter segments SES. Theoretical analysis and simulation results show the HSES can obtain the optimal performance tradeoff between end-to-end delay and classical cost.

A closed-loop BMI system design based on the improved SJIT model and the network of Izhikevich neurons

Brain–machine interface (BMI) is a useful technology which creates a new way for disable people to communicate with the world, but experimenting with human brains is risky. Hence, a precise mathematical model of the information transmission in the process of limb movement is necessary to be established. In this paper, firstly, we improve the classical single-joint information transmission (SJIT) model through introducing several neuron models, and the improved model is closer to the true single-joint movements. Secondly, a closed-loop system with a Wiener filter-based decoder, an auxiliary controller based on model predictive control (MPC) and a network of Izhikevich neurons is formulated based on the improved model, and the used network of Izhikevich neurons is more time efficient than the existing one. Finally, in this closed-loop system, the intracortical micro-stimulation (ICMS) technology is introduced to feedback the information from the MPC controller in real time. The auxiliary controller assist the brain to control artificial arm by changing the frequency of stimulation current. In this way, the computational complexity of the optimization problem proposed in this paper is greatly reduced, and the closed-loop BMI system designed in this paper can well track the desired trajectory.

Performance analysis of quantum channels

We study the quality of service in quantum channels. We regard the quantum channel as a queueing system, and present queueing analysis of both the classical information transmission and quantum information transmission in the quantum channel. For the former, we link the analysis to the classical queueing model, and for the latter, we propose a new queueing model and investigate the limit queueing behavior. For both scenarios, we obtain tail distributions of the performance measures, that is, backlog, delay, and throughput.

A closed-loop brain–machine interface framework design for motor rehabilitation

Brain–machine interfaces (BMIs) can be adopted to rehabilitate motor systems for disabled subjects by sensing cortical neuronal activities and creating new method. In this paper, to achieve the function of motor rehabilitation, two generalized BMI frameworks, including decoders, encoders and auxiliary controllers, are proposed and compared based on a classical single-joint information transmission model. Firstly, a decoder based on the Wiener filter and an encoder based on a network of spiking neurons are designed to compensate for the absent information pathway, and a charge-balanced intra-cortical microstimulation current is chosen as the input of the spiking neuron network; Secondly, to formulate closed-loop BMI frameworks, two auxiliary controllers are designed according to the strategy of model predictive control, where the controller inputs are the position of joint muscle trajectories and the average firing activity trajectories of perceived position vector neurons. Thirdly, considering that several integer parameters are included in the charge-balanced intra-cortical microstimulation current and that the optimization problem for solving the control inputs also includes these decision variables, a particle swarm optimization algorithm is adopted to solve the hard optimization problem. We compare the motor recovery effectiveness of the two presented frameworks through these simulations and choose the better framework for future BMI system design. The proposed frameworks provide a important theoretical guidance for designing BMI system applied in future life.

Sending classical information via three noisy channels in superposition of causal orders

In this work, we study the transmission of classical information through three completely depolarizing channels in superposition of different causal orders. We thus introduce the quantum 3-switch as a resource for quantum communications. We perform a new kind of quantum control that was not accessible to the previously treated two-channel case. The fine and full quantum control achieved using selected combinations of causal orders let us uncover new features: non monotonous behavior on the transmission of information with respect to the number of causal orders involved, and different values of the transmission of information depending on the specific combinations of causal orders considered. Our results are a stepping stone to assess efficiency of coherent quantum control and optimize resources in the implementation of new indefinite causal structures. Finally, we suggest an optical implementation using standard telecom technology to test our predictions.

Continuous-variable quantum network coding protocol based on butterfly network model

With the development of quantum network, quantum continuous-variables have practical significance of improving communication. This paper proposes a new continuous-variable quantum network coding protocol (CVQNC) based on the butterfly network model with the hybrid channel of quantum channel and classical channel to realise the cross transmission of quantum information and classical information. The new protocol not only is conducive to the realisation of quantum network, but also can reduce the communication cost of quantum network effectively. It can be seen from the throughput and fidelity analysis that this protocol has a higher throughput than discrete-variable quantum network encoding scheme and classical information network encoding scheme. The ceiling of fidelity in this protocol is 4/9. According to the analysis of simple intercept attack and spectroscope attack, it is secure for the protocol to transmit quantum information and classical information by resisting on the eavesdropping attack of the third-party effectively.

P.737 Cocaine alters the gut microbiome in a self-administration rat model: Reversal by dehydroepiandrosterone treatment

Brain–machine interface (BMI) is a useful technology which creates a new way for disable people to communicate with the world, but experimenting with human brains is risky. Hence, a precise mathematical model of the information transmission in the process of limb movement is necessary to be established. In this paper, firstly, we improve the classical single-joint information transmission (SJIT) model through introducing several neuron models, and the improved model is closer to the true single-joint movements. Secondly, a closed-loop system with a Wiener filter-based decoder, an auxiliary controller based on model predictive control (MPC) and a network of Izhikevich neurons is formulated based on the improved model, and the used network of Izhikevich neurons is more time efficient than the existing one. Finally, in this closed-loop system, the intracortical micro-stimulation (ICMS) technology is introduced to feedback the information from the MPC controller in real time. The auxiliary controller assist the brain to control artificial arm by changing the frequency of stimulation current. In this way, the computational complexity of the optimization problem proposed in this paper is greatly reduced, and the closed-loop BMI system designed in this paper can well track the desired trajectory.