HKU Scholars Hubhttp://hub.hku.hkThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sat, 01 Oct 2022 15:51:13 GMT2022-10-01T15:51:13Z501391- Superfluid inside neutron stars and their signature of existencehttp://hdl.handle.net/10722/34804Title: Superfluid inside neutron stars and their signature of existence
Authors: Chau, Hoi-fung.; 周海峰
Wed, 01 Jan 1992 00:00:00 GMThttp://hdl.handle.net/10722/348041992-01-01T00:00:00Z
- Local measurements are sufficient to obtain maximal information on independently prepared quantum stateshttp://hdl.handle.net/10722/59631Title: Local measurements are sufficient to obtain maximal information on independently prepared quantum states
Authors: Fung, CHF; Chau, HF
Abstract: Given a composite quantum system in which the states of the subsystems are independently (but not necessarily identically) prepared, we construct separate measurements on the subsystems from any given joint measurement such that the former always give at least as much information as the latter. This construction offers insights into the understanding of measurements on this type of composite system. Moreover, this construction essentially proves the intuition that separate measurements on the subsystems are sufficient to extract the maximal information about the separately prepared subsystems, thus making a joint measurement unnecessary. Furthermore, our result implies that individual attacks are as powerful as collective attacks in obtaining information about the raw key in quantum key distribution. © 2008 The American Physical Society.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10722/596312008-01-01T00:00:00Z
- Induced metric and matrix inequalities on unitary matriceshttp://hdl.handle.net/10722/145919Title: Induced metric and matrix inequalities on unitary matrices
Authors: Chau, HF; Li, CK; Poon, YT; Sze, NS
Abstract: Recently, Chau (2011 Quantum Inform. Comput. 11 721) showed that one can define certain metrics and pseudo-metrics on U(n), the group of all n × n unitary matrices, based on the arguments of the eigenvalues of the unitary matrices. More importantly, these metrics and pseudo-metrics have quantum information theoretical meanings. So it is instructive to study this kind of metrics and pseudo-metrics on U(n). Here we show that any symmetric norm on ℝ n induces a metric on U(n). Furthermore, using the same technique, we prove an inequality concerning the eigenvalues of a product of two unitary matrices which generalizes a few inequalities obtained earlier by Chau (arXiv:1006.3614v1). © 2012 IOP Publishing Ltd.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1459192012-01-01T00:00:00Z
- A new decoy state technique with more than three photon intensitieshttp://hdl.handle.net/10722/253702Title: A new decoy state technique with more than three photon intensities
Authors: Chau, HF
Abstract: Decoy state is now a standard method to close the loophole of quantum cryptography
using Poisson sources. It uses three photon intensities to do the job. One of the
difficulties in decoy-state quantum key distribution (QKD) is that it is not possible to determine
precisely the values of Yn’s, namely the yield for n photon events because apparently
one has to invert a matrix with large condition number in the process. This, in return, limits
the provably secure key rate. Here I show that this comment is not completely correct.
Specifically, one could still improve the provably secure key rate without worrying about
numerical stability. I demonstrate my finding through an example of using more than three
photon intensities in performing decoy-state QKD.
This work is supported by the RGC Grant of the HKSAR Government.
Reference: H. F. Chau, Phys. Rev. A 97, 040301R (2018).
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2537022018-01-01T00:00:00Z
- Elementary proofs of two theorems involving arguments of eigenvalues of a product of two unitary matriceshttp://hdl.handle.net/10722/139652Title: Elementary proofs of two theorems involving arguments of eigenvalues of a product of two unitary matrices
Authors: Chau, HF; Lam, YT
Abstract: We give elementary proofs of two theorems concerning bounds on the maximum argument of the eigenvalues of a product of two unitary matrices--one by Childs et al. [J. Mod. Phys. 47, 155 (2000)] and the other one by Chau [Quant. Inf. Comp. 11, 721 (2011)]. Our proofs have the advantages that the necessary and sufficient conditions for equalities are apparent and that they can be readily generalized to the case of infinite-dimensional unitary operators. © 2011 Chau and Lam; licensee Springer.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1396522011-01-01T00:00:00Z
- Parity problem with a cellular automaton solutionhttp://hdl.handle.net/10722/43328Title: Parity problem with a cellular automaton solution
Authors: Lee, KM; Xu, H; Chau, HF
Abstract: The parity of a bit string of length N is a global quantity that can be efficiently computed using a global counter in O(N) time. But is it possible to find the parity using cellular automata with a set of local rule tables without using any global counter? Here, we report a way to solve this problem using a number of r=1 binary, uniform, parallel, and deterministic cellular automata applied in succession for a total of O(N2) time.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10722/433282001-01-01T00:00:00Z
- Time-energy costs of quantum measurementshttp://hdl.handle.net/10722/198069Title: Time-energy costs of quantum measurements
Authors: Fung, FCH; Chau, HF
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/1980692014-01-01T00:00:00Z
- Quantum speed limit with forbidden speed intervalshttp://hdl.handle.net/10722/186161Title: Quantum speed limit with forbidden speed intervals
Authors: Chau, HF
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1861612013-01-01T00:00:00Z
- Measuring time-energy resources for quantum processeshttp://hdl.handle.net/10722/190222Title: Measuring time-energy resources for quantum processes
Authors: Fung, FCH; Chau, HF
Abstract: The speed of any quantum process is limited by quantum mechanics via time-energy uncertainty relations and they imply that time and energy are tradeoff with each other. As such, we propose to measure the time-energy as a single unit for quantum channels. We consider a time-energy measure for quantum channels and compute lower and upper bounds of it using the channel Kraus operators. For a special class of channels (which includes the depolarizing channel), we obtain the exact value of the time-energy measure. Our result can be used to compare the time-energy resources of similar quantum processes. In particular, we show that erasing quantum information requires √(n + 1)/n) times more time-energy resource than erasing classical information, where n is the system dimension. This work is published in [1].
Description: Parallel Session B
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1902222013-01-01T00:00:00Z
- Relation between physical time-energy cost of a quantum process and its information fidelityhttp://hdl.handle.net/10722/203317Title: Relation between physical time-energy cost of a quantum process and its information fidelity
Authors: Fung, FCH; Chau, HF
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2033172014-01-01T00:00:00Z
- Disguising quantum channels by mixing and channel distance trade-offhttp://hdl.handle.net/10722/195693Title: Disguising quantum channels by mixing and channel distance trade-off
Authors: Fung, FCH; Chau, HF
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/1956932014-01-01T00:00:00Z
- Solution to Time-energy Costs of Quantum Channelshttp://hdl.handle.net/10722/208704Title: Solution to Time-energy Costs of Quantum Channels
Authors: Fung, CHF; Chau, HF; Li, CK; Sze, NS
Abstract: We derive a formula for the time-energy costs of general quantum channels proposed in [Phys. Rev. A 88, 012307 (2013)]. This formula allows us to numerically find the time-energy cost of any quantum channel using positive semidefinite programming. We also derive a lower bound to the time-energy cost for any channels and the exact the time-energy cost for a class of channels which includes the qudit depolarizing channels and projector channels as special cases.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2087042015-01-01T00:00:00Z
- Incorporating inertia into multiagent systemshttp://hdl.handle.net/10722/146332Title: Incorporating inertia into multiagent systems
Authors: Man, WC; Chau, HF
Abstract: We consider a model that demonstrates the crucial role of inertia and stickiness in multiagent systems, based on the minority game. The inertia of an agent is introduced into the game model by allowing agents to apply hypothesis testing when choosing their best strategies, thereby reducing their reactivity toward changes in the environment. We find by extensive numerical simulations that our game shows a remarkable improvement of global cooperation throughout the whole phase space. In other words, the maladaptation behavior due to over-reaction of agents is removed. These agents are also shown to be advantageous over the standard ones, which are sometimes too sensitive to attain a fair success rate. We also calculate analytically the minimum amount of inertia needed to achieve the above improvement. Our calculation is consistent with the numerical simulation results. Finally, we review some related works in the field that show similar behaviors and compare them to our work. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/1463322006-01-01T00:00:00Z
- Quantum key distribution with delayed privacy amplification and its application to the security proof of a two-way deterministic protocolhttp://hdl.handle.net/10722/145929Title: Quantum key distribution with delayed privacy amplification and its application to the security proof of a two-way deterministic protocol
Authors: Fung, CHF; Ma, X; Chau, HF; Cai, QY
Abstract: Privacy amplification (PA) is an essential postprocessing step in quantum key distribution (QKD) for removing any information an eavesdropper may have on the final secret key. In this paper, we consider delaying PA of the final key after its use in one-time pad encryption and prove its security. We prove that the security and the key generation rate are not affected by delaying PA. Delaying PA has two applications: it serves as a tool for significantly simplifying the security proof of QKD with a two-way quantum channel, and also it is useful in QKD networks with trusted relays. To illustrate the power of the delayed PA idea, we use it to prove the security of a qubit-based two-way deterministic QKD protocol which uses four states and four encoding operations. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1459292012-01-01T00:00:00Z
- Quantum string seal is insecurehttp://hdl.handle.net/10722/45272Title: Quantum string seal is insecure
Authors: Chau, HF
Abstract: A quantum string seal encodes the value of a (bit) string as a quantum state in such a way that everyone can extract a non-negligible amount of available information on the string by a suitable measurement. Moreover, such measurement must disturb the quantum state and is likely to be detected by an authorized verifier. In this way, the intactness of the encoded quantum state plays the role of a wax seal in the digital world. Here we analyze the security of quantum string seal by studying the information disturbance trade-off of a measurement. This information disturbance trade-off analysis extends the earlier results of Bechamann-Pasquinucci, Dâ€™Ariano, and Macchiavello [Int. J. Quant. Inform. 3, 435 (2005)] and Chau [Phys. Lett. A 354, 31 (2006)] by concluding that all quantum string seals are insecure. Specifically, we find a way to obtain nontrivial available information on the string that escapes the verifierâ€™s detection with at least 50% chance. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/452722007-01-01T00:00:00Z
- On the rotation and magnetic field evolution of superconducting strange starshttp://hdl.handle.net/10722/43192Title: On the rotation and magnetic field evolution of superconducting strange stars
Authors: Chau, HF
Abstract: Are pulsars made up of strange matter? The magnetic field decay of a pulsar may be able to give us an answer. Since Cooper pairing of quarks occurs inside a sufficiently cold strange star, the strange stellar core is superconducting. In order to compensate for the effect of rotation, different superconducting species inside a rotating strange star try to set up different values of London fields. Thus we have a frustrated system. Using Ginzburg-Landau formalism, I solved the problem of a rotating superconducting strange star: Instead of setting up a global London field, vortex bundles carrying localized magnetic fields are formed. Moreover, the number density of vortex bundles is directly proportional to the angular speed of the star. Since it is energetically favorable for the vortex bundles to pin to magnetic flux tubes, the rotational dynamics and magnetic evolution of a strange star are coupled together, leading to magnetic flux expulsion as the star slows down. I investigate this effect numerically and find that the characteristic field decay time is much less than 20 Myr in all reasonable parameter regions. On the other hand, the characteristic magnetic field decay time for pulsars is ≥ 20 Myr. Thus, my finding casts doubts on the hypothesis that pulsars are strange stars. © 1997. The American Astronomical Society. All rights reserved.
Wed, 01 Jan 1997 00:00:00 GMThttp://hdl.handle.net/10722/431921997-01-01T00:00:00Z
- Practical entanglement distillation scheme using recurrence method and quantum low density parity check codeshttp://hdl.handle.net/10722/145044Title: Practical entanglement distillation scheme using recurrence method and quantum low density parity check codes
Authors: Chau, HF; Ho, KH
Abstract: Many entanglement distillation schemes use either universal random hashing or breeding as their final step to obtain almost perfect shared EPR pairs spite of a high yield, the hardness of decoding a random linear code makes the use of random hashing and breeding infeasible in practice this pilot study, we analyze the performance of the recurrence method, a well-known entanglement distillation scheme, with its final random hashing or breeding procedure being replaced by various efficiently decodable quantum codes. Among all the replacements investigated, the one using a certain adaptive quantum low density parity check (QLDPC) code is found to give the highest yield for Werner states over a wide range of noise level- the yield for using this QLDPC code is higher than the first runner up by more than 25% over a wide parameter range this respect, the effectiveness of using QLDPC codes in practical entanglement distillation is illustrated. © The Author(s) 2010.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1450442011-01-01T00:00:00Z
- Tight upper bound of the maximum speed of evolution of a quantum statehttp://hdl.handle.net/10722/123858Title: Tight upper bound of the maximum speed of evolution of a quantum state
Authors: Chau, HF
Abstract: I report a tight upper bound of the maximum speed of evolution from one quantum state ρ to another ρ′ with fidelity F(ρ,ρ′) less than or equal to an arbitrary but fixed value under the action of a time-independent Hamiltonian. Since the bound is directly proportional to the average absolute deviation from the median of the energy of the state DE, one may interpret DE as a meaningful measure of the maximum information-processing capability of a system. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1238582010-01-01T00:00:00Z
- Quantum convolutional error-correcting codeshttp://hdl.handle.net/10722/43234Title: Quantum convolutional error-correcting codes
Authors: Chau, HF
Abstract: I report two general methods to construct quantum convolutional codes for N-state quantum systems. Using these general methods, I construct a quantum convolutional code of rate 1/4, which can correct one quantum error for every eight consecutive quantum registers.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10722/432341998-01-01T00:00:00Z
- Practical issues in quantum-key-distribution postprocessinghttp://hdl.handle.net/10722/80667Title: Practical issues in quantum-key-distribution postprocessing
Authors: Fung, CHF; Ma, X; Chau, HF
Abstract: Quantum key distribution (QKD) is a secure key generation method between two distant parties by wisely exploiting properties of quantum mechanics. In QKD, experimental measurement outcomes on quantum states are transformed by the two parties to a secret key. This transformation is composed of many logical steps (as guided by security proofs), which together will ultimately determine the length of the final secret key and its security. We detail the procedure for performing such classical postprocessing taking into account practical concerns (including the finite-size effect and authentication and encryption for classical communications). This procedure is directly applicable to realistic QKD experiments and thus serves as a recipe that specifies what postprocessing operations are needed and what the security level is for certain lengths of the keys. Our result is applicable to the BB84 protocol with a single or entangled photon source. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/806672010-01-01T00:00:00Z
- Classifying rational densities using two one-dimensional cellular automatahttp://hdl.handle.net/10722/43217Title: Classifying rational densities using two one-dimensional cellular automata
Authors: Chau, HF; Yan, KK; Wan, KY; Siu, LW
Abstract: Given a (finite but arbitrarily long) string of zeros and ones, we report a way to determine if the number of ones is less than, greater than, or equal to a prescribed number by applying two sets of cellular automation rules in succession. Thus, we solve the general one-dimensional density classification problem using two cellular automata.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10722/432171998-01-01T00:00:00Z
- Cellular automaton model for diffusive and dissipative systemshttp://hdl.handle.net/10722/43173Title: Cellular automaton model for diffusive and dissipative systems
Authors: Chan, TC; Chau, HF; Cheng, KS
Abstract: We study a cellular automaton model which allows diffusion of energy (or equivalently any other physical quantities such as mass of a particular compound) at every lattice site after each time step. A unit amount of energy is randomly added onto a site. Whenever the local energy content of a site reaches a fixed threshold Ec1, energy will be dissipated. The dissipation of energy propagates to the neighboring sites provided that the energy contents of those sites are greater than or equal to another fixed threshold Ec2 (≤Ec1). Under such dynamics, the system evolves into three different types of states depending on the values of Ec1 and Ec2 as reflected in their dissipation size distributions, namely, localized peaks, power laws, or exponential laws. This model is able to describe the behaviors of various physical systems including the statistics of burst sizes and burst rates in type-I x-ray bursters. Comparisons between our model and the famous forest-fire model are made. © 1995 The American Physical Society.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10722/431731995-01-01T00:00:00Z
- Postglitch relaxation of the Crab pulsar after its first four major glitches: The combined effects of crust cracking, formation of vortex depletion region and vortex creephttp://hdl.handle.net/10722/43170Title: Postglitch relaxation of the Crab pulsar after its first four major glitches: The combined effects of crust cracking, formation of vortex depletion region and vortex creep
Authors: Alpar, MA; Chau, HF; Cheng, KS; Pines, D
Abstract: Following the application of vortex creep theory (Alpar et al. 1984; Alpar et al. 1993; Chau et al. 1993) to the postglitch behavior of the Vela pulsar, we extend the model to cover the postglitch behavior of the Crab pulsar (Alpar et al. 1994). We propose that the comparatively modest (ΔΩ/Ω ∼ 10 -8) and somewhat infrequent (∼6 yr interglitch intervals) Crab pulsar glitches are caused by crust cracking during starquakes induced by pulsar spin-down (Ruderman 1976; Baym & Pines 1971). We attribute the anomalous postglitch behavior (an occasional extended spin-up and a long-term response opposite in sign to that seen in the Vela pulsar [see Lyne, Graham-Smith, & Pritchard 1992]) to postglitch response to inward vortex bunching into newly formed vortex traps during a quake. The persistent shift in the angular acceleration Ω c following a glitch is attributed to the creation of a new vortex depletion region (Alpar & Pines 1993). The different postglitch behavior for the Crab and Vela pulsars can be understood on evolutionary grounds (Alpar et al. 1994). © 1996. The American Astronomical Society. All rights reserved.
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/10722/431701996-01-01T00:00:00Z
- Quantum-classical complexity-security tradeoff in secure multiparty computationshttp://hdl.handle.net/10722/43287Title: Quantum-classical complexity-security tradeoff in secure multiparty computations
Authors: Chau, HF
Abstract: I construct a secure multiparty scheme to compute a classical function by a succinct use of a specially designed fault-tolerant random polynomial quantum error correction code. This scheme is secure provided that (asymptotically) strictly more than five-sixths of the players are honest. Moreover, the security of this scheme follows directly from the theory of quantum error correcting code, and hence is valid without any computational assumption. I also discuss the quantum-classical complexity-security tradeoff in secure multiparty computation schemes and argue why a full-blown quantum code is necessary in my scheme.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/432872000-01-01T00:00:00Z
- Unconditionally secure key distribution in higher dimensions by depolarizationhttp://hdl.handle.net/10722/43470Title: Unconditionally secure key distribution in higher dimensions by depolarization
Authors: Chau, HF
Abstract: This paper presents a prepare-and-measure scheme using N-dimensional quantum particles as information carriers where N is a prime power. One of the key ingredients used to resist eavesdropping in this scheme is to depolarize all Pauli errors introduced to the quantum information carriers. Using the Shor-Preskill-type argument, we prove that this scheme is unconditionally secure against all attacks allowed by the laws of quantum physics. For N = 2n > 2, each information carrier can be replaced by n entangled qubits. In this case, there is a family of eavesdropping attacks on which no unentangled-qubit-based prepare-and-measure (PM) quantum key distribution scheme known to date can generate a provably secure key. In contrast, under the same family of attacks, our entangled-qubit-based scheme remains secure whenever 2n ≥ 4. This demonstrates the advantage of using entangled particles as information carriers and of using depolarization of Pauli errors to combat eavesdropping attacks more drastic than those that can be handled by unentangled-qubit-based prepare-and-measure schemes. © 2005 IEEE.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10722/434702005-01-01T00:00:00Z
- State-independent error-disturbance trade-off for measurement operatorshttp://hdl.handle.net/10722/225651Title: State-independent error-disturbance trade-off for measurement operators
Authors: Zhou, SS; Wu, S; Chau, HF
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2256512016-01-01T00:00:00Z
- Decoy-state quantum key distribution with more than three types of photon intensity pulseshttp://hdl.handle.net/10722/252213Title: Decoy-state quantum key distribution with more than three types of photon intensity pulses
Authors: Chau, HF
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2522132018-01-01T00:00:00Z
- Purifying Greenberger-Horne-Zeilinger states using degenerate quantum codeshttp://hdl.handle.net/10722/59591Title: Purifying Greenberger-Horne-Zeilinger states using degenerate quantum codes
Authors: Ho, KH; Chau, HF
Abstract: Degenerate quantum codes are codes that do not reveal the complete error syndrome. Their ability to conceal the complete error syndrome makes them powerful resources in certain quantum-information processing tasks. In particular, the most error-tolerant way to purify depolarized Bell states using one-way communication known to date involves degenerate quantum codes. Here we study three closely related purification schemes for depolarized Greenberger-Horne-Zeilinger states shared among m≥3 players by means of degenerate quantum codes and one-way classical communications. We find that our schemes tolerate more noise than all other one-way schemes known to date, further demonstrating the effectiveness of degenerate quantum codes in quantum-information processing. © 2008 The American Physical Society.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10722/595912008-01-01T00:00:00Z
- Self-organized critical model of biological evolutionhttp://hdl.handle.net/10722/174847Title: Self-organized critical model of biological evolution
Authors: Chau, HF; Mak, L; Kwok, PK
Abstract: A punctuated equilibrium model of biological evolution with relative fitness between different species being the fundamental driving force of evolution is introduced. Mutation is modeled as a fitness updating cellular automation process where the change in fitness after mutation follows a Gaussian distribution with mean x > 0 and standard deviation σ. Scaling behaviors are observed in our numerical simulation, indicating that the model is self-organized critical. Besides, the numerical experiment suggests that models with different x and σ belongs to the same universality class. © 1995.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10722/1748471995-01-01T00:00:00Z
- Scaling behavior of the punctuated-equilibrium model of evolutionhttp://hdl.handle.net/10722/174888Title: Scaling behavior of the punctuated-equilibrium model of evolution
Authors: Chau, HF
Abstract: The existence of scaling behavior in real physical time in the punctuated-equilibrium model of evolution proposed recently from Bak and Sneppen [Phys. Rev. Lett. 71, 4083 (1993)] is assured provided that the characteristic mutation time of a species varies exponentially with its fitness. A self-consistent condition on the characteristic fitness is also derived. © 1994 The American Physical Society.
Sat, 01 Jan 1994 00:00:00 GMThttp://hdl.handle.net/10722/1748881994-01-01T00:00:00Z
- An alternative proof of some percolation threshold (pc) using the idea of self-organized criticalityhttp://hdl.handle.net/10722/175152Title: An alternative proof of some percolation threshold (pc) using the idea of self-organized criticality
Authors: Chau, HF; Cheng, KS
Abstract: By means of a well-developed method in self-organized criticality, we can obtain the lower bound for the percolation threshold (pc) of the corresponding site percolation problem. In some special cases, we have proved that such lower bounds are indeed the percolation thresholds. We can reproduce some well-known percolation thresholds of various lattices including the Cayley trees and Kock curves in this framework. © 1994 Società Italiana di Fisica.
Sat, 01 Jan 1994 00:00:00 GMThttp://hdl.handle.net/10722/1751521994-01-01T00:00:00Z
- Generalized sandpile model and the characterization of the existence of self-organized criticalityhttp://hdl.handle.net/10722/175094Title: Generalized sandpile model and the characterization of the existence of self-organized criticality
Authors: Chau, HF; Cheng, KS
Abstract: We consider a generalized sandpile model where the particle addition and toppling are formulated in terms of mappings. In this way, the toppling rules and toppling conditions of the system can also be completely general. Even under these extremely relaxed conditions, we can still find an if and only if condition for the existence of an absolute steady state. Moreover, such a kind of absolute steady state often exhibits self-organized criticality. Our model is a superset of both the original Bak-Tang-Wiesenfeld sandpile and the Abelian sandpile models. Finally, we shall demonstrate the importance of both the particle-addition methods and the boundary conditions to the self-organized critical phenomena of a physical system. © 1991 The American Physical Society.
Tue, 01 Jan 1991 00:00:00 GMThttp://hdl.handle.net/10722/1750941991-01-01T00:00:00Z
- Self-organized critical models without local particle conservation laws on superlatticeshttp://hdl.handle.net/10722/175098Title: Self-organized critical models without local particle conservation laws on superlattices
Authors: Chau, HF
Abstract: We consider simple examples of self-organized critical systems on one-dimensional superlattices without local particle conservation laws. The set of all recurrence states are also found in these examples using a method similar to the burning algorithm.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10722/1750981995-01-01T00:00:00Z
- N-dimensional Abelian sandpile model with nearest-neighbor topplinghttp://hdl.handle.net/10722/175082Title: N-dimensional Abelian sandpile model with nearest-neighbor toppling
Authors: Chau, HF; Cheng, KS
Abstract: We have derived an exact expression for the determinant of the toppling matrix of the Abelian sandpile model in any finite dimension with open boundary conditions. The result can also apply to the semiopen boundary cases in certain limiting cases. An analytic result can also be obtained in the thermodynamic limit where the grid size tends to infinite: namely, the total number of system configurations in the self-organized critical state follows a power law as the grid size increases. Therefore, under a uniform but random particle addition, 1/f2 instead of 1/f scaling is observed. The relation with the site percolation problem is also discussed. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/10722/1750821993-01-01T00:00:00Z
- Generalized Abelian sandpile modelhttp://hdl.handle.net/10722/175132Title: Generalized Abelian sandpile model
Authors: Chau, HF
Abstract: A sufficient condition for which the particle addition operations commute in the eventual phase space of a class of sandpile models with either integral or real local heights are obtained. In case the local heights take on real numbers, the volume of the eventual phase space is found to be ≤|detΔ| under the usual Lebesgue measure, which extends the earlier result by Dhar for the integral case. The geometrical aspect of the results, including the effect on the avalanche size distribution, are also discussed. © 1994.
Sat, 01 Jan 1994 00:00:00 GMThttp://hdl.handle.net/10722/1751321994-01-01T00:00:00Z
- Inverse avalanches on Abelian sandpileshttp://hdl.handle.net/10722/175084Title: Inverse avalanches on Abelian sandpiles
Authors: Chau, HF
Abstract: A simple and computationally efficient way of finding inverse avalanches for Abelian sandpiles, called the inverse particle addition operator, is presented. In addition, the method is shown to be optimal in the sense that it requires the minimum amount of computation among methods of the same kind. The method is also conceptually succinct because avalanche and inverse avalanche are placed in the same footing. © 1994 The American Physical Society.
Sat, 01 Jan 1994 00:00:00 GMThttp://hdl.handle.net/10722/1750841994-01-01T00:00:00Z
- On the avalanche-finiteness of Abelian Sandpileshttp://hdl.handle.net/10722/174986Title: On the avalanche-finiteness of Abelian Sandpiles
Authors: Chan, SW; Chau, HF
Abstract: We prove a necessary and sufficient condition for an Abelian Sandpile Model (ASM) to be avalanche-finite, namely: all unstable states of the system can be brought back to stability in finite number of topplings. The method is also computationally feasible since it involves no greater than O(N 3) arithmetic computations where N is the total number of sites of the system. © 1995.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/10722/1749861995-01-01T00:00:00Z
- Comment on Quantum convolutional error-correcting codeshttp://hdl.handle.net/10722/174975Title: Comment on Quantum convolutional error-correcting codes
Authors: De Almeida, ACA; Palazzo, R; Chau, HF
Abstract: In this Comment we present a counterexample to theorems 2 and 3 from Chau [Phys. Rev. A 58, 905 (1998)] regarding quantum convolutional codes. © 2005 The American Physical Society.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10722/1749752005-01-01T00:00:00Z
- Postglitch relaxation of the Crab pulsar: Evidence for crust crackinghttp://hdl.handle.net/10722/174907Title: Postglitch relaxation of the Crab pulsar: Evidence for crust cracking
Authors: Alpar, MA; Chau, HF; Cheng, KS; Pines, D
Abstract: The pattern of glitches and postglitch behavior observed for the Crab pulsar (Boynton et al. 1972; Demiański & Prószyński 1983; Lyne & Pritchard 1987; Lyne, Graham-Smith, & Pritchard 1992) is strikingly different from that observed for the Vela pulsar (Alpar et al. 1993). A key question is whether the differences can be understood on evolutionary grounds. An analysis of the Crab pulsar suggests that this is indeed the case. Thus, we propose that the comparatively modest (ΔΩ/Ω ∼ 10 -8) and somewhat infrequent (∼6 yr interglitch intervals) Crab pulsar glitches are caused by starquakes induced by pulsar spin-down (Ruderman 1976; Baym & Pines 1971); we attribute its anomalous postglitch behavior (an occasional extended spin-up and a long-term response opposite in sign to that seen in the Vela pulsar (Lyne et al. 1992) to vortices transported inward during a quake, while the observed unexpected persistent change in angular acceleration, Ω̇ e, following a glitch represents the creation of a new vortex depletion region, as suggested by Alpar & Pines (1993).
Sat, 01 Jan 1994 00:00:00 GMThttp://hdl.handle.net/10722/1749071994-01-01T00:00:00Z
- Correlated creep rate of a vortex line under the effect of vortex tension and its relation to the glitches of pulsarshttp://hdl.handle.net/10722/175005Title: Correlated creep rate of a vortex line under the effect of vortex tension and its relation to the glitches of pulsars
Authors: Chau, HF; Cheng, KS
Abstract: In our earlier works, we have calculated the correlated creep velocity of a vortex line with line tension, which is pinned to a perfect simple-cubic lattice, and creeps out under the action of a biased potential by thermal activation. In this paper, we extend the result to cases in which the biased potential, the line tension, and the pinning energy of the line are all functions of position. Although an evaluation of the exact correlated creep velocity is difficult, a good approximate form can be found. We show that the Anderson-Kim thermal-activation formula in the vortex-creep model is still valid after suitable modification even though their uncorrelated-creeping assumption is incorrect. We apply our formalism to study the motion of vortex lines in the crustal region of neutron stars. The model results suggests that the steady-state configuration of vortex lines should form a set of hyperbolic-like curves because the stronger-pinning regions (which also have higher tension) are located in the inner regions of the crust. Perturbations, like a star quake, can cause a large number of vortex lines to unpin from the stronger-pinning region and the tension forces the vortex lines to move by a macroscopic distance. Such a mechanism may be responsible for the glitches of pulsars. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/10722/1750051993-01-01T00:00:00Z
- Path-integral method of solving the problem of thermal vortex creephttp://hdl.handle.net/10722/175007Title: Path-integral method of solving the problem of thermal vortex creep
Authors: Chau, HF; Cheng, KS
Abstract: The path-integral approach is adopted to investigate the motion of vortex lines that are pinned to the crystal lattice and creep thermally against the pinning energy barriers. The thermal creeping process of the entire vortex line is correlated by the presence of vortex tension. Our model results are applicable to a vast number of physical phenomena including the magnetic vortices in type-II superconductors and the superfluid vortices in neutron stars. © 1991 The American Physical Society.
Tue, 01 Jan 1991 00:00:00 GMThttp://hdl.handle.net/10722/1750071991-01-01T00:00:00Z
- Implications of3P2 superfluidity in the interior of neutron starshttp://hdl.handle.net/10722/174901Title: Implications of3P2 superfluidity in the interior of neutron stars
Authors: Chau, HF; Cheng, KS; Ding, KY
Abstract: The magnetized vortex lines of the 3P2 paired neutron superfluid are effectively pinned by the magnetic energy barriers produced by the flux tubes of the 1S0 paired proton superconducting fluid. The stellar crust and the core superfluid can be coupled primarily via thermal vortex creep against the barriers. We study the postglitch relaxation of the core superfluid by using the thermal vortex creep model in the limit where the motion of flux tubes is slow compared with that of the vortex lines. Our model results impose some serious constraints on the strength of the core magnetic field, the internal temperature of the star, and the interaction between neutrons and protons in the regime of nuclear matter density.
Wed, 01 Jan 1992 00:00:00 GMThttp://hdl.handle.net/10722/1749011992-01-01T00:00:00Z
- Getting information on independently prepared quantum states: when are individual measurements as powerful as joint measurements?http://hdl.handle.net/10722/165682Title: Getting information on independently prepared quantum states: when are individual measurements as powerful as joint measurements?
Authors: Fung, FCH; Chau, HF
Abstract: Given a composite quantum system in which the states of the subsystems are independently (but not necessarily identically) prepared, we construct separate measurements on the subsystems from any given joint measurement such that the former always give at least as large information as the latter. This construction offers new insights into the understanding of measurements on this type of composite systems. Moreover, this construction essentially proves the intuition that separate measurements on the subsystems are sufficient to extract the maximal information about the separately prepared subsystems, thus making a joint measurement unnecessary. Furthermore, our result implies that individual attacks are as powerful as collective attacks in obtaining information on the raw key in quantum key distribution.
Description: Session Y17: Focus Session: Quantum Metrology and Nanomechanics: abstract ID: BAPS.2009.MAR.Y17.4
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/1656822009-01-01T00:00:00Z
- On a universal squash model of quantum signal detectionhttp://hdl.handle.net/10722/165681Title: On a universal squash model of quantum signal detection
Authors: Chau, HF; Fung, FCH
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/1656812009-01-01T00:00:00Z
- Finding the sign of a function value by binary cellular automatonhttp://hdl.handle.net/10722/132506Title: Finding the sign of a function value by binary cellular automaton
Authors: Chau, HF; Had, XU; Lee, KM; Siu, LW; Yan, KK
Abstract: Given a continuous function f(x), suppose that the sign of f has only finitely many discontinuous points in the interval [0, 1]. We show how to use a sequence of one-dimensional deterministic binary cellular automata to determine the sign of f(ρ) where ρ is the (number) density of 1s in an arbitrarily given bit string of finite length provided that f satisfies certain technical conditions.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10722/1325062002-01-01T00:00:00Z
- Quantum key distribution with delayed privacy amplification and its application to security proof of a two-way deterministic protocolhttp://hdl.handle.net/10722/165678Title: Quantum key distribution with delayed privacy amplification and its application to security proof of a two-way deterministic protocol
Authors: Fung, FCH; Ma, X; Chau, HF; Cai, QY
Abstract: Privacy amplification (PA) is an essential post-processing step in quantum key distribution (QKD) for removing any information an eavesdropper may have on the final secret key. In this paper, we consider delaying PA of the final key after its use in one-time pad encryption and prove its security. We prove that the security and the key generation rate is not affected by delaying PA. Delaying PA has two applications: it serves as a tool for significantly simplifying the security proof of QKD with a two-way quantum channel, and also it is useful in QKD networks with trusted relays. To illustrate the power of the delayed PA idea, we use it to prove the security of a qubit-based two-way deterministic QKD protocol which uses four states and four encoding operations.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1656782012-01-01T00:00:00Z
- An improved upper bound for the critical car density of the two-dimensional Biham-Middleton-Levine traffic modelhttp://hdl.handle.net/10722/80592Title: An improved upper bound for the critical car density of the two-dimensional Biham-Middleton-Levine traffic model
Authors: Chau, HF; Wan, KY; Yan, KK
Abstract: By means of non-linear dynamics, we show that the critical car densities of both the two-dimensional Biham-Middleton-Levine and the green wave traffic models are strictly less than 1/2. © 1998 Elsevier Science B.V. All rights reserved.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10722/805921998-01-01T00:00:00Z
- 香港中學文憑考試: 物理精讀 3http://hdl.handle.net/10722/145652Title: 香港中學文憑考試: 物理精讀 3; Physics: study guide for HKDSEE 3
Authors: Chau, HF; Wong, CM; Ng, TK; Leung, YC; Leung, KH; Yu, KW
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1456522011-01-01T00:00:00Z
- Magnetic Field Evolution of a Superconducting Strange Starhttp://hdl.handle.net/10722/109723Title: Magnetic Field Evolution of a Superconducting Strange Star
Authors: Chau, HF; Tang, CKL
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10722/1097231998-01-01T00:00:00Z
- Entanglement distillation by quantum low density parity codes – A preliminary studyhttp://hdl.handle.net/10722/109724Title: Entanglement distillation by quantum low density parity codes – A preliminary study
Authors: Ho, KH; Chau, HF
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/1097242007-01-01T00:00:00Z