arXiv subjects

Qing-Yu Cai

Publications and source records attributed to Qing-Yu Cai.

6 recordsLinked to original sources

arXiv2023

Improving the performance of twin-field quantum key distribution with advantage distillation technology

In this work, we apply the advantage distillation method to improve the performance of a practical twin-field quantum key distribution system under collective attack. Compared with the previous analysis result given by Maeda, Sasaki and Koashi [Nature Communication 10, 3140 (2019)], the maximal transmission distance obtained by our analysis method will be increased from 420 km to 470 km. By increasing the loss-independent misalignment error to 12%, the previous analysis method can not overcome the rate-distance bound. However, our analysis method can still overcome the rate-distance bound when the misalignment error is 16%. More surprisingly, we prove that twin-field quantum key distribution can generate positive secure key even if the misalignment error is close to 50%, thus our analysis method can significantly improve the performance of a practical twin-field quantum key distribution system.

quant-ph↗

arXiv2018

High fidelity quantum cloning of two known nonorthogonal quantum states via weak measurement

We propose a scheme to enhance the fidelity of symmetric quantum cloning machine using a weak measurement. By adjusting the intensity of weak measurement parameter $p$, we obtain the copies with different optimal fidelity. Choosing proper value of $p$, we can obtain the perfect copies for initial qubits. In this paper, we focus on $1-2$ quantum cloning for two nonorthogonal states. Sets containing more than two linear independent states are also discussed briefly. Due to weak measurements being probabilistic, we obtain high fidelity at risk of probability. If the weak measurement successes, we do the following operations to obtain copies with high fidelity, otherwise, the cloning process fails and we need do nothing. From this perspective, the scheme we propose is economical for saving quantum resource and time, which may be very useful in quantum information processing.

quant-ph↗

arXiv2018

Non-thermal radiation of black hole off canonical typicality

We study the Hawking radiation of black holes by considering the canonical typicality. For the universe consisting of black holes and their outer part, we directly obtain a non-thermal radiation spectrum of an arbitrary black hole from its entropy, which only depends on a few external qualities (known as hairs), such as mass, charge, and angular momentum. Our result shows that the spectrum of the non-thermal radiation is independent of the detailed quantum tunneling dynamics across black hole horizon. We prove that the black hole information paradox is naturally resolved by taking account the correlation between black hole and its radiation in our approach.

quant-ph↗

arXiv2004

Information Erasure and Recover in Quantum Memory

We show that information in quantum memory can be erased and recovered perfectly if it is necessary. That the final states of environment are completely determined by the initial states of the system allows that an easure operation can be realized by a swap operation between system and an ancilla. Therefore, the erased information can be recoverd. When there is an irreversible process, e.g. an irreversible operation or a decoherence process, in the erasure process, the information would be erased perpetually. We present that quantum erasure will also give heat dissipation in environment. And a classical limit of quantum erasure is given which coincides with Landauer's erasure principle.

quant-ph↗

arXiv2004

N-Partner Secure Direct Communication Based on Quantum Nonlocality

A multipartner secure direct communication protocol is presented, using quantum nonlocality. Security of this protocol is based on `High fidelity implies low entropy'. When the entanglement was successfully distributed, anyone of the multipartner can send message secretly by using local operation and reliable public channel. Since message transfered only by using local operation and public channel after entanglement successfully distributed, so this protocol can protect the communication against destroying-travel-qubit-type attack.

quant-ph↗

arXiv2003

Measurement, Trace, Information Erasure and Entropy

We show that both information erasure process and trace process can be realized by projective measurement. And a partial trace operation consists to a projective measurement on a subsystem. We show that a nonunitary operation will destroy the wave-behavior of a particle. We give a quantum manifestation of Maxwell's demon and give a quantum manifestation of the second law of therodynamics. We show that, considering the law of memontum-energy conversation, the evolution of a closed system should be unitary and the von Neumann entropy of the closed quantum system should be least.

quant-ph↗