arXiv subjects

Chang-Pu Sun

Publications and source records attributed to Chang-Pu Sun.

At least 19 recordsLinked to original sources

arXiv2026

Nonorthogonal-state erasure as the resource behind apparent second-law violations

Perfect deterministic distinguishing of nonorthogonal quantum states is forbidden by the linear and unitary structure of quantum mechanics. It has often been assumed that, if such distinguishing were available, it would be the resource enabling work extraction from a single heat bath. We show that this expectation identifies the wrong thermodynamic operation and prove such hypothetical operation increases, rather than decreases, the joint entropy of system and detector. The entropy-decreasing resource is instead the inverse operation, which we call nonorthogonal-state erasure. Reanalyzing a Peres-type Szilard engine, we show that the apparent extracted work $W_{\mathrm{ext}}=0.2766k_{\mathrm{B}}T$ for an equal mixture of an atomic ensemble with spin state $\left|\uparrow\right\rangle $ and $\left|\rightarrow\right\rangle $. Thus the apparent second-law violation is supplied not by nonorthogonal-state distinguishing, but by a nonorthogonal quantum state erasure.

quant-ph↗

arXiv2024

The emergence of Newtonian mechanics from the inhomogeneity of an ensemble

To address the observation of Max Born (M. Born 1969) that the Newton's second law can emerge from a purely statistical perspective, we derive the evolution equation about the statistical distribution for dilute gas based solely on statistical principles, without invoking Newtonian mechanics, and then obtain the equations of motion for individual particles. Newton's second law for a single particle naturally emerges when the distribution reaches equilibrium. We demonstrate that the magnitude of an external force, traditionally measured by particle acceleration, can be understood as a measure of distribution inhomogeneity. We further show that the entropic force (utilized in current gravity studies) is equivalent to the statistical force and under non-equilibrium conditions, a deviation arises between the entropic force and the Newtonian force. This framework offers a novel perspective distinct from classical Newtonian mechanics and broadens the potential scope of its application.

cond-mat.stat-mech↗

arXiv2022

Dark Information in Black Hole with $λφ$ Fluid

It has been shown that the nonthermal spectrum of Hawking radiation will lead to information-carrying correlations between emitted particles in the radiation. The mutual information carried by such correlations can not be locally observed and hence is dark. With dark information, the black hole information is conserved. In this paper, we look for the spherically symmetric black hole solution in a $λφ$ fluid model and investigate the radiation spectrum and dark information of the black hole. The spacetime structure of this black hole is similar to that of the Schwarzschild one, while its horizon radius is decreased by the $λφ$ fluid. By using the statistical mechanical method, the nonthermal radiation spectrum is calculated. This radiation spectrum is very different from the Schwarzschild case at its last stage because of the effect of the $λφ$ fluid. The $λφ$ fluid reduces the lifetime of the black hole, but increases the dark information of the Hawking radiation.

gr-qc↗

arXiv2021

Hierarchical Coarse-grained Approach to the Duration-dependent Spreading Dynamics in Complex Networks

Various coarse-grained models have been proposed to study the spreading dynamics in the network. A microscopic theory is needed to connect the spreading dynamics with the individual behaviors. In this letter, we unify the description of different spreading dynamics on complex networks by decomposing the microscopic dynamics into two basic processes, the aging process and the contact process. A microscopic dynamical equation is derived to describe the dynamics of individual nodes on the network. The hierarchy of a duration coarse-grained (DCG) approach is obtained to study duration-dependent processes, where the transition rates depend on the duration of an individual node on a state. Applied to the epidemic spreading, such formalism is feasible to reproduce different epidemic models, e.g., the susceptible-infected-recovered and the susceptible-infected-susceptible models, and to associate with the corresponding macroscopic spreading parameters with the microscopic transition rate. The DCG approach enables us to obtain the steady state of the general SIS model with arbitrary duration-dependent recovery and infection rates. The current hierarchical formalism can also be used to describe the spreading of information and public opinions, or to model a reliability theory in networks.

cond-mat.stat-mech↗

arXiv2020

Quantifying Algebraic Asymmetry of Hamiltonian Systems

The symmetries play important roles in physical systems. We study the symmetries of a Hamiltonian system by investigating the asymmetry of the Hamiltonian with respect to certain algebras. We define the asymmetry of an operator with respect to an algebraic basis in terms of their commutators. Detailed analysis is given to the Lie algebra $\mathfrak{su}(2)$ and its $q$-deformation. The asymmetry of the $q$-deformed integrable spin chain models is calculated. The corresponding geometrical pictures with respect to such asymmetry is presented.

quant-ph↗

arXiv2019

Universal trapping law induced by atomic cloud in single-photon cooperative dynamics

Single-photon cooperative dynamics of an assembly of two-level quantum emitters coupled by a bosonic bath are investigated. The bosonic bath is general and it can be anything as long as the exchange of excitations between quantum emitters and bath is present. In these systems, it is found that the population on the excited emitter keeps a simple and universal trapping law due to the existence of system's dark states. Different from the trapping regime caused by photonemitter dressed states, this type of trapping is only associated with the number of quantum emitters. According to the trapping law, the cooperative spontaneous emission at single-photon level in this kind of systems is universally inhibited when the emitter number is large enough.

quant-ph↗

arXiv2019

Experimental validation of the $1/τ$ -scaling entropy generation in finite-time thermodynamics with dry air

The second law of thermodynamics can be described as the non-decreasing of the entropy in the irreversible thermodynamic process. Such phenomenon can be quantitatively evaluated with the irreversible entropy generation (IEG), which was recently found to follow a $1/τ$ scaling for the system under a long contact time $τ$ with the thermal bath. This scaling, predicted in many finite-time thermodynamic models, is of great potential in the optimization of heat engines, yet remains lack of direct experimental validation. In this letter, we design an experimental apparatus to test such scaling by compressing dry air in a temperature-controlled water bath. More importantly, we quantitatively verify the optimized control protocol to reduce the IEG. Such optimization shall bring new insight to the practical design of heat engine cycles.

cond-mat.stat-mech↗

arXiv2019

Achieve Higher Efficiency at Maximum Power with Finite-time Quantum Otto Cycle

The optimization of finite-time thermodynamic heat engines was intensively explored recently, yet limited to few cycles, e.g. finite-time Carnot-like cycle. In this paper, we supplement a new type of finite-time engine with quantum Otto cycle and show the better performance. The current model can be widely utilized benefited from the general \mathcal{C}/τ^{2} scaling of extra work for finite-time adiabatic process with long control time τ. Such scaling allows analytical optimization of the generic finite-time quantum Otto cycle to surpass the efficiency at maximum power for the Carnot-like engine. We apply the current perturbation method to the quantum piston model and calculate the efficiency at maximum power, which is validated with exact solution.

quant-ph↗

arXiv2019

Controlling single-photon scattering in a rectangular waveguide by a V-type three-level emitter

The single-photon scattering in a rectangular waveguide by a V-type three-level emitter is studied for large range of input-photon energy beyond the single-mode region. By using Lippmann-Schwinger formalism, the necessary and sufficient conditions of complete transmission and complete reflection are derived analytically. In the single-mode region, the complete transmission caused by electromagnetically induced transparency (EIT) and the complete reflection due to Fano resonance can both be achieved by adjusting the emitter's parameters. But in the multi-mode region, except that the input-state is prepared in a coherent superposition state, the perfect reflection is absent, and the photon inevitably enters other propagation modes due to the indirectly interaction between waveguide modes mediated by the emitter. Other remarkable features in the photon transport induced by the finite cross section includes the blueshift of the reflection resonance and the cutoff-frequency effect.

quant-ph↗

arXiv2019

Directional quantum random walk induced by coherence

Quantum walk (QW), which is considered as the quantum counterpart of the classical random walk (CRW), is actually the quantum extension of CRW from the single-coin interpretation. The sequential unitary evolution engenders correlation between different steps in QW and leads to a ballistic position distribution. In this paper, we propose an alternative quantum extension of CRW from the ensemble interpretation, named quantum random walk (QRW), where the walker has many unrelated coins, modeled as two-level systems, initially prepared in the same state. We calculate the walker's position distribution in QRW for different initial coin states with the coin operator chosen as Hadamard matrix. In one-dimensional case, the walker's position is the asymmetric binomial distribution. We further demonstrate that in QRW, coherence leads the walker to perform directional movement. For an initially decoherenced coin state, the walker's position distribution is exactly the same as that of CRW. Moreover, we study QRW in 2D lattice, where the coherence plays a more diversified role in the walker's position distribution.

quant-ph↗

arXiv2019

Boosting the performance of the Quantum Otto heat engines

To optimize the performance of a heat engine in finite-time cycle, it is important to understand the finite-time effect of thermodynamic processes. Previously, we have shown that extra work is needed to complete a quantum adiabatic process in finite time, and proved that the extra work follows a \mathcal{C}/τ^{2} scaling for long control time τ. There the oscillating part of the extra work is neglected due to the complex energy-level structure of the particular quantum system. However, such oscillation of the extra work can not be neglected in some quantum systems with simple energy-level structure, e. g. the two-level system or the quantum harmonic oscillator. In this paper, we build the finite-time quantum Otto engine on these simple systems, and find that the oscillating extra work leads to a jagged edge in the constraint relation between the output power and the efficiency. By optimizing the control time of the quantum adiabatic processes, the oscillation in the extra work is utilized to enhance the maximum power and the efficiency. We further design special control schemes with the zero extra work at the specific control time. Compared to the linear control scheme, these special control schemes of the finite-time adiabatic process improve the maximum power and the efficiency of the finite-time Otto engine.

quant-ph↗

arXiv2019

Uncertainties of genuinely incompatible triple measurements based on statistical distance

We investigate the measurement uncertainties of a triple of positive operator-valued measures (POVMs) based on statistical distance, and formulate state-independent tight uncertainty inequalities satisfied by the three measurements in terms of triple-wise joint measurability. Particularly, uncertainty inequalities for three unbiased qubit measurements are presented with analytical lower bounds which relates to the necessary and sufficient condition of the triple-wise joint measurability of the given triple. We show that the measurement uncertainties for a triple measurement are essentially different from the ones obtained by pair wise measurement uncertainties by comparing the lower bounds of different measurement uncertainties.

quant-ph↗

arXiv2018

Universal constraint for efficiency and power of a low-dissipation heat engine

The constraint relation for efficiency and power is crucial to design optimal heat engines operating within finite time. We find a universal constraint between efficiency and output power for heat engines operating in the low-dissipation regime. Such constraint is validated with an example of Carnot-like engine. Its microscopic dynamics is governed by the master equation. Based on the master equation, we connect the microscopic coupling strengths to the generic parameters in the phenomenological model. We find the usual assumption of low-dissipation is achieved when the coupling to thermal environments is stronger than the driving speed. Additionally, such connection allows the design of practical cycle to optimize the engine performance.

quant-ph↗

arXiv2018

Optimal operating protocol to achieve efficiency at maximum power of heat engines

The efficiency at maximum power has been investigated extensively, yet the practical control scheme to achieve it remains elusive. We fill such gap with a stepwise Carnot-like cycle, which consists the discrete isothermal process (DIP) and adiabatic process. With DIP, we validate the widely adopted assumption of \mathscr{C}/t relation of the irreversible entropy generation S^{(\mathrm{ir})}, and show the explicit dependence of the coefficient \mathscr{C} on the fluctuation of the speed of tuning energy levels as well as the microscopic coupling constants to the heat baths. Such dependence allows to control the irreversible entropy generation by choosing specific control schemes. We further demonstrate the achievable efficiency at maximum power and the corresponding control scheme with the simple two-level system. Our current work opens new avenues for the experimental test, which was not feasible due to the lack the of the practical control scheme in the previous low-dissipation model or its equivalents.

quant-ph↗

arXiv2018

The Bose-Fermi duality in quantum Otto heat engine with trapped repulsive Bosons

Quantum heat engine with ideal gas has been well studied, yet the role of interaction was seldom explored. We construct a quantum Otto heat engine with N repulsive Bosonic particles in a 1D hard wall box. With the advantage of exact solution using Bethe Ansatz, we obtain not only the exact numerical result of efficiency in all interacting strength c, but also analytical results for strong interaction. We find the efficiency ηrecovers to the one of non-interacting case $η_{\mathrm{non}}=1-(L_{1}/L_{2})^{2}$ for strong interaction with asympotic behavior $η\simη_{\mathrm{non}}-4(N-1)L_{1}\left(L_{2}-L_{1}\right)/(cL_{2}^{3})$. Here, $L_{1}$ and $L_{2}$ are two trap sizes during the cycle. Such recovery reflects the duality between 1D strongly repulsive Bosons and free Fermion. We observe and explain the appearance of a minimum efficiency at a particular interacting strength c, and study its dependence on the temperature.

quant-ph↗

arXiv2018

Quantum sensing enhanced by adaptive periodic quantum control

Using a single quantum probe to sense other quantum objects offers distinct advantages but suffers from some limitations that may degrade the sensing precision severely, especially when the probe-target coupling is weak. Here we propose a strategy to improve the sensing precision by using the quantum probe to engineer the evolution of the target. We consider an exactly solvable model, in which a qubit is used as the probe to sense the frequency of a harmonic oscillator. We show that by applying adaptive periodic quantum control on the qubit, the sensing precision can be enhanced from 1/T scaling with the total time cost T to 1/T^{2} scaling, thus improving the precision by several orders of magnitudes. Such improvement can be achieved without any direct access to the oscillator and the improvement increases with decreasing probe-target coupling. This provides a useful routine to ultrasensitive quantum sensing of weakly coupled quantum objects.

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↗

arXiv2018

Dark information of black hole radiation raised by dark energy

The "lost" information of black hole through the Hawking radiation was discovered being stored in the correlation among the non-thermally radiated particles [Phys. Rev. Lett 85, 5042 (2000), Phys. Lett. B 675, 1 (2009)]. This correlation information, which has not yet been proved locally observable in principle, is named by dark information. In this paper, we systematically study the influences of dark energy on black hole radiation, especially on the dark information. Calculating the radiation spectrum in the existence of dark energy by the approach of canonical typicality, which is reconfirmed by the quantum tunneling method, we find that the dark energy will effectively lower the Hawking temperature, and thus makes the black hole has longer life time. It is also discovered that the non-thermal effect of the black hole radiation is enhanced by dark energy so that the dark information of the radiation is increased. Our observation shows that, besides the mechanical effect (e.g., gravitational lensing effect), the dark energy rises the the stored dark information, which could be probed by a non-local coincidence measurement similar to the coincidence counting of the Hanbury-Brown -Twiss experiment in quantum optics.

gr-qc↗