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Chi-Yee Cheung

Publications and source records attributed to Chi-Yee Cheung.

At least 19 recordsLinked to original sources
arXiv2023

Unconditionally secure quantum bit commitment using modified double-slit and unstable particles

We note that the proof of the no-go theorem of unconditionally secure quantum bit commitment is based on a model which is not universal. For protocols not described by the model, this theorem does not apply. Using unstable particles and a modified double-slit setup, we construct such a protocol and show that it is unconditionally secure. In this protocol, the committer transfers no quantum states to the receiver.

quant-ph↗
arXiv2019

On the question of secret probability distributions in quantum bit commitment

The proof of the No-Go Theorem of unconditionally secure quantum bit commitment depends on the assumption that Alice knows every detail of the protocol, including the probability distributions associated with all the random variables generated by Bob. We argue that this condition may not be universally satisfied. In fact it can be shown that when Bob is allowed to use a secret probability distribution, the joint quantum state is inevitably mixed. It is then natural to ask if Alice can still cheat. A positive answer has been given by us [13] for the perfect concealing case. In this paper, we present a simplified proof of our previous result, and extend it to cover the imperfect concealing case as well.

quant-ph↗
arXiv2016

Heavy-Flavor-Conserving Hadronic Weak Decays of Heavy Baryons

More than two decades ago, we studied heavy-flavor-conserving weak decays of heavy baryons within the framework that incorporates both heavy-quark and chiral symmetries. In view of the first observation of $Ξ_b^-\toΛ_b^0π^-$ by LHCb recently, we have reexamined these decays and presented updated predictions. The predicted rates for $Ξ_b^-\toΛ_b^0π^-$ in the MIT bag and diquark models are consistent with experiment. The major theoretical uncertainty stems from the evaluation of baryon matrix elements. The branching fraction of $Ξ_c\toΛ_cπ$ is predicted to be of order $10^{-4}$. It is suppressed relative to $Br(Ξ_b\toΛ_bπ)$ owing to the shorter lifetime of $Ξ_c$ relative to $Ξ_b$ and the destructive nonspectator $W$-exchange contribution. The kinematically accessible weak decays of the sextet heavy baryon $Ω_Q$ are $Ω_Q\toΞ_Qπ$. Due to the absence of the $B_6-B_{\bar 3}$ transition in the heavy quark limit and the $B_6-B_6$ transition in the model calculations, $Ω_Q\toΞ_Qπ$ vanish in the heavy quark limit.

hep-ph↗
arXiv2016

Three symmetry breakings in strong and radiative decays of strange heavy mesons

In this paper, we investigate three symmetry breaking effects in strong and radiative decays of strange heavy mesons. We study 1/m_Q corrections within the heavy quark effect theory, as well as SU(3) and SU(2) symmetry breakings induced by light quark mass differences and the η-πmixing vertex. These effects are studied in a covariant model. The numerical results show that the 1/m_Q corrections of the coupling constants are consistent with α_s Λ_{QCD}/m_Q. The SU(3) symmetry violating effect of the strong coupling constant is obviously larger than that of the magnetic coupling constant. The value of the η-πmixing vertex has some changes because of the renewed data. As compared with the other theoretical calculations and the experimental data, our radiative decay rates are much larger than those of the other theoretical methods, except for \chiPT; however, our branching ratios are close to the experimental data.

hep-ph↗
arXiv2015

Quantum bit commitment using Wheeler's delayed choice experiment

We construct a quantum bit commitment scheme using a double-slit setup similar to Wheeler's delayed choice experiment. Bob sends photons toward the double-slit, and Alice commits by determining either the slit from which each photon emerges (for $b=0$), or its landing position on a screen (for $b=1$). Since the photon's wave front expands at the speed of light, Alice cannot delay the detection indefinitely, or it would very soon be out of her control no matter how much resources she has.

quant-ph↗
arXiv2014

Strong and radiative decays of heavy mesons in a covariant model

In this paper, we investigate symmetry breaking effects in strong and radiative decays of heavy mesons. We study $1/m_Q$ corrections within the heavy quark effective theory. These effects are studied in a covariant model for heavy mesons. The numerical results are consistent with the experimental data and some other theoretical calculations. These provide a vote of confidence for the validity of this covariant model.

hep-ph↗
arXiv2014

Unconditionally secure bit commitment by causally independent encryptions

We propose a new classical bit commitment protocol using the relativistic constraint that signals cannot travel faster than the speed of light $c$. This protocol is unconditionally secure against both classical or quantum attacks. The sender (Alice) and the receiver (Bob) each controls two secure stations separated by a large distance $d$, and they communicate by exchanging classical information only. Alice commits by sending from her stations two causally independent encrypted messages to the neighboring Bob's stations, after that the protocol is out of her control and she plays no role in the unveiling phase. The commitment remains concealed for a period of $Δt=d/2c$. This protocol requires only limited communication resources and is readily implementable with current technologies.

quant-ph↗
arXiv2010

Unconditionally Secure Quantum Bit Commitment Using Neutron Double-Slit Interference

Using a neutron double-slit setup, we construct a quantum bit commitment scheme in which time development of quantum states plays an essential role. Our scheme evades the widely accepted no-go theorem by the fact that it is neither possible to stop the time evolution of spreading wave packets, nor is it possible to evolve them backward in time. Moreover, for unstable particles such as neutrons, one cannot delay detecting their positions indefinitely, or they would disintegrate spontaneously and escape detection. We find that using non-stationary states instead of stationary ones, unconditionally secure quantum bit commitment is possible.

quant-ph↗
arXiv2009

Criterion for faithful teleportation with an arbitrary multiparticle channel

We consider quantum teleportation when the given entanglement channel is an arbitrary multiparticle state. A general criterion is presented, which allows one to judge if the channel can be used to teleport faithfully an arbitrary quantum state of a given dimension. The general protocol proposed here is much easier to implement experimentally than the others found in the literature.

quant-ph↗
arXiv2008

Minimal classical communication and measurement complexity for quantum information splitting

We present two quantum information splitting schemes using respectively tripartite GHZ and asymmetric W states as quantum channels. We show that, if the secret state is chosen from a special ensemble and known to the sender (Alice), then she can split and distribute it to the receivers Bob and Charlie by performing only a single-qubit measurement and broadcasting an one-cbit message. It is clear that no other schemes could possibly achieve the same goal with simpler measurement and less classical communication. In comparison, existing schemes work for arbitrary quantum states which need not be known to Alice, however she is required to perform a two-qubit Bell measurement and communicate a two-cbit message. Hence there is a trade off between flexibility and measurement complexity plus classical resource. In situations where our schemes are applicable, they will greatly reduce the measurement complexity and at the same time cut the communication overhead by one half.

quant-ph↗
arXiv2006

Controlled Quantum Secret Sharing

We present a new protocol in which a secret multiqubit quantum state $\ketΨ$ is shared by $n$ players and $m$ controllers, where $\ketΨ$ is the encoding state of a quantum secret sharing scheme. The players may be considered as field agents responsible for carrying out a task, using the secret information encrypted in $\ketΨ$, while the controllers are superiors who decide if and when the task should be carried out and who to do it. Our protocol only requires ancillary Bell states and Bell-basis measurements.

quant-ph↗
arXiv2006

Secure Quantum Bit Commitment Using Unstable Particles

Using unstable particles which decay by emitting neutrinos, we propose a quantum bit commitment protocol that is humanly impossible to break. Neutrinos carry away quantum information, but their interaction with matter is so weak that it would take an astronomically-sized machine just to catch them, not to mention performing controlled unitary operations on them. As a result quantum information is lost, and cheating is not possible even if the participants had access to the most powerful quantum computers that could ever be built. Therefore, for all practical purposes, our new protocol is as good as unconditionally secure.

quant-ph↗
arXiv2006

Insecurity of Quantum Bit Commitment with Secret Parameters

The impossibility proof of unconditionally secure quantum bit commitment is crucially dependent on the assertion that Bob is not allowed to generate probability distributions unknown to Alice. This assertion is actually not meaningful, because Bob can always cheat without being detected. In this paper we prove that, for any concealing protocol involving secret probability distributions, there exists a cheating unitary transformation that is known to Alice. Our result closes a gap in the original impossibility proof.

quant-ph↗
arXiv2005

Secret parameters in quantum bit commitment

The no-go theorem of unconditionally secure quantum bit commitment depends crucially on the assumption that Alice knows in detail all the probability distributions generated by Bob. We show that if a protocol is concealing, then the cheating unitary transformation is independent of any parameters (including probability distributions) secretly chosen by Bob, so that Alice can calculate it without knowing Bob's secret choices. Otherwise the protocol cannot be concealing. Our result shows that the original impossibility proof was based on an incorrect assumption, despite the fact that its conclusion remains valid within the adopted framework. Furthermore, our result eliminates a potential loophole in the no-go theorem.

quant-ph↗
arXiv2005

The generalized parton distributions of the nucleon in the NJL model based on the Faddeev approach

We study the generalized parton distributions, including the helicity-flip ones, using Nambu-Jona-Lasinio model based on a relativistic Faddeev approach with `static approximation'. Sum rules relating the generalized parton distributions to nucleon electromagnetic form factors are satisfied. Moreover, quark-antiquark contributions in the region $-ξ<x<ξ$ are non-vanishing. Our results are qualitatively similar to those calculated with Radyushkin's double distribution ansatz using forward parton distribution functions calculated in the NJL model as inputs.

hep-ph↗
arXiv2003

Quantum Bit Commitment can be Unconditionally Secure

It is generally believed that unconditionally secure quantum bit commitment (QBC) is proven impossible by a "no-go theorem". We point out that the theorem only establishes the existence of a cheating unitary transformation in any QBC scheme secure against the receiver, but this fact alone is not sufficient to rule out unconditionally secure QBC as a matter of principle, because there exists no proof that the cheating unitary transformation must be known to the cheater in all possible cases. In this work, we show how to circumvent the "no-go theorem" and prove that unconditionally secure QBC is in fact possible.

quant-ph↗