Quantum Channel States Research Articles

Convenient quantum controlled teleportation of two-qubit pure state with seven-qubit entangled state

Based on a seven-qubit entangled state, Chen et al (2020 Int. J. Theor. Phys. 59 1402) presented a scheme for controlled quantum teleportation. Using the same quantum channel state, we put forward a new scheme in which the quantum information sender can also transmit a Bell state to receiver under the agreement and assist of the controller. The comparison with Chen et al’s scheme is made and reveals its distinct advantage of reducing the classical resource consumption and increasing the intrinsic efficiency as well as degrading the complexity of necessary operations.

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.

Quantum Channel State Masking

Communication over a quantum channel that depends on a quantum state is considered when the encoder has channel side information (CSI) and is required to mask information on the quantum channel state from the decoder. A full characterization is established for the entanglement-assisted masking equivocation region with a maximally correlated channel state, and a regularized formula is given for the quantum capacity-leakage function without assistance. For Hadamard channels without assistance, we derive single-letter inner and outer bounds, which coincide in the standard case of a channel that does not depend on a state.

An adaptive quantum state-hopping communication strategy based on kangaroo entanglement hopping model

Quantum communication in free space will be disturbed by natural environment such as fog and dust. However, to build a global quantum satellite wide area communication network, we must solve the problem of 24-h all-weather communication between satellite and earth. With the evolution of time, the degree of interference becomes deeper. In order to improve the performance of quantum communication under such an interference, in this paper we analyze the change of single quantum state channel over time under the background interference, and propose an quantum state-hopping communication strategy based on the kangaroo entanglement hopping model (KEHM), and simulate the performance and parameters of the strategy. Kangaroos are social animals. When they are frightened, they will jump synchronously in the same way with the same step length, height and frequency. According to this model, we make the two communicating parties realize synchronous quantum state jump according to the prearranged pattern. The simulations show that when the ratio between the average power of background quantum noise and the average power of quantum signal is 5, the quantum bit error rate decreases from 0.4524 to 0.1116 with the quantum state hopping frequency increasing from 1 to 15. When the single quantum state transmission success rate is 0.95 and the quantum bit rate is greater than 200 qubit/s, the probabilities of successful transmission of quantum bits at different state hopping frequencies are greater than 0.97. When the quantum reception efficiency of the receiver is 0.8, the quantum state pass rate increases from 0.3667 to 0.9986 with the average quantum number of the source increasing from 1 to 10. When the average quantum number of the source is 6, the passing rate of quantum state increases from 0.6262 to 0.9855 with the quantum receiving efficiency of the receiver increasing from 0.2 to 0.99. However, if the average quantum number of the transmitter is large enough and the receiving efficiency of the receiver is close to 1, the passing rate of the quantum state is also close to 1. The adaptive control strategy of quantum state hopping is based on real-time quantum channel state detection. Its core idea is to remove the quantum states which are seriously disturbed from the quantum state hopping set, and to realize the synchronous hopping of communication parties on the quantum states with low interference. Adopting the strategy of quantum state hopping adaptive control can further reduce the quantum bit error rate of the system. The error rate gain of adaptive control system increases with the increase of the success probability of processing the disturbed quantum state. When the probability of processing the disturbed quantum state is 0.95, the system error rate gain can reach 1.301. The performance of quantum state hopping system is improved obviously. To sum up, the adaptive quantum state-hopping communication strategy based on the kangaroo entanglement hopping model proposed in this paper greatly enhances the comprehensive immunity of the system and ensures the security of quantum information network, and provides an important reference for the healthy development of wide-area quantum satellite communication network in the future.

On Landauer’s Principle and Bound for Infinite Systems

Landauer's principle provides a link between Shannon's information entropy and Clausius' thermodynamical entropy. We set up here a basic formula for the incremental free energy of a quantum channel, possibly relative to infinite systems, naturally arising by an Operator Algebraic point of view. By the Tomita-Takesaki modular theory, we can indeed describe a canonical evolution associated with a quantum channel state transfer. Such evolution is implemented both by a modular Hamiltonian and a physical Hamiltonian, the latter being determined by its functoriality properties. This allows us to make an intrinsic analysis, extending our QFT index formula, but without any a priori given dynamics; the associated incremental free energy is related to the logarithm of the Jones index and is thus quantised. This leads to a general lower bound for the incremental free energy of an irreversible quantum channel which is half of the Landauer bound, and to further bounds corresponding to the discrete series of the Jones index. In the finite dimensional context, or in the case of DHR charges in QFT, where the dimension is a positive integer, our lower bound agrees with Landauer's bound.

Bidirectional Teleportation Protocol in Quantum Wireless Multi-hop Network

We propose a bidirectional quantum teleportation protocol based on a composite GHZ-Bell state. In this protocol, the composite GHZ-Bell state channel is transformed into two-Bell state channel through gate operations and single qubit measurements. The channel transformation will lead to different kinds of quantum channel states, so a method is proposed to help determine the unitary matrices effectively under different quantum channels. Furthermore, we discuss the bidirectional teleportation protocol in the quantum wireless multi-hop network. This paper is aimed to provide a bidirectional teleportation protocol and study the bidirectional multi-hop teleportation in the quantum wireless communication network.

Strong Converse for the Classical Capacity of Entanglement-Breaking and Hadamard Channels via a Sandwiched Rényi Relative Entropy

A strong converse theorem for the classical capacity of a quantum channel states that the probability of correctly decoding a classical message converges exponentially fast to zero in the limit of many channel uses if the rate of communication exceeds the classical capacity of the channel. Along with a corresponding achievability statement for rates below the capacity, such a strong converse theorem enhances our understanding of the capacity as a very sharp dividing line between achievable and unachievable rates of communication. Here, we show that such a strong converse theorem holds for the classical capacity of all entanglement-breaking channels and all Hadamard channels (the complementary channels of the former). These results follow by bounding the success probability in terms of a “sandwiched” Rényi relative entropy, by showing that this quantity is subadditive for all entanglement-breaking and Hadamard channels, and by relating this quantity to the Holevo capacity. Prior results regarding strong converse theorems for particular covariant channels emerge as a special case of our results.

Effect of Dissipative Environments on Atomic-State Quantum Teleportation

In the paper, taking the atomic EPR entanglement states as quantum channel, we investigate the fidelity of quantum teleportation of atomic state in thermal environment and vacuum reservoir by means of quantum theory of damping-density operator approach, and the average fidelities are calculated, the results show that the atomic quantum channel state is more robust than in teleportation process when they are subject to the dissipative environments.

Remote Preparation of an Entangled State in NonidealConditions

In this paper, the theoretical investigation of remote preparation of anentangled state is studied in nonideal conditions. Our studies include twoparts. In the first part, we consider the remote state preparation (RSP) ofan entangled state through two equally noisy quantum channel states, namely,a mixture of Bell states. Studies show there is a particular mixed-statechannel for which all pure entangled states remain entangled after thisinexact RSP. In the second part, we suppose that noises which quantum channelssuffer from can be expressed as the Lindblad operators. The master equationof the system can be expressed in the Lindblad form. Through solving themaster equation, we calculate the fidelity as a function of decoherencerates and parameters of the state to be prepared. For a given entangledstate, we investigate the influence of different types of noises on the fidelity.

Entanglement swapping of two-mode Gaussian states in a thermal environment

Entanglement swapping of two-mode Gaussian states is investigated by use of quantum teleportation protocol of continuous variables. In the entanglement swapping protocol, we take the two-mode squeezed vacuum which is exposed in a thermal environment as a mixed-quantum-channel state and a two-mode standard form Gaussian state as an input state to be teleported. When the input state is pure, we find that the swapped state is inseparable if and only if both the input state and the quantum-channel state are entangled. When the input state is mixed and entangled, we find that the swapped state is inseparable only if the quantum-channel state is sufficiently much entangled. We also notice that the required minimum entanglement in the mixed quantum channel to maintain entanglement in the swapped state strongly depends on the global purity of the input state.