arXiv subjects

C. P. Sun

Publications and source records attributed to C. P. Sun.

At least 55 records · Page 3Linked to original sources

arXiv2021

Spatial enantioseparation of gaseous chiral molecules

We explore the spatial enantioseparation of gaseous chiral molecules for the cyclic three-level systems coupled with three electromagnetic fields. Due to molecular rotations, the specific requirements of the polarization directions of the three electromagnetic fields lead to the space-dependent part of the overall phase of the coupling strengths. Thus, the overall phase of the coupling strengths, which differs with $π$ for the enantiomers in the cyclic three-level model of chiral molecules, varies intensely in the length scale of the typical wavelength of the applied electromagnetic fields. Under the induced gauge potentials resulting from the space-dependent part of the overall phase and the space-dependent intensities of coupling strengths, we further show spatial enantioseparation for typical parameters of gaseous chiral molecules.

physics.atom-ph↗

arXiv2021

Geodesic path for the minimal energy cost in shortcuts to isothermality

Shortcut to isothermality is a driving strategy to steer the system to its equilibrium states within finite time, and enables evaluating the impact of a control promptly. Finding optimal scheme to minimize the energy cost is of critical importance in applications of this strategy in pharmaceutical drug test, biological selection, and quantum computation. We prove the equivalence between designing the optimal scheme and finding the geodesic path in the space of control parameters. Such equivalence allows a systematic and universal approach to find the optimal control to reduce the energy cost. We demonstrate the current method with examples of a Brownian particle trapped in controllable harmonic potentials.

cond-mat.stat-mech↗

arXiv2021

Works with quantum resource of coherence

We study the modification of the second law of thermodynamics for a quantum system interacting with a reservoir regarding quantum coherence. The whole system is isolated so that neither energy nor information is lost. It is discovered that the coherence of the reservoir can serves as a useful resource allowing the system extract more energy from the reservoir; among the coherence measures, only is the relative entropy of coherence feasible to quantitatively characterize energy exchange. We demonstrate that a thermodynamic cycle between two coherent reservoirs can output more work than its classical counterpart. The efficiency of such cycle surpasses the Carnot efficiency, which is the upper bound of heat engine efficiency in classical regime.

quant-ph↗

arXiv2021

Enantio-specific state transfer for symmetric-top chiral molecules

We study the enantio-specific state transfer in a four-level model for symmetric-top chiral molecules. Such a model is formed by coupling the electric-dipole transitions among four appropriate working states with three electromagnetic fields. It includes two cyclic three-level substructures, where the overall phases differ by $π$ with enantiomers and reflect the chirality dependence of the molecule. Based on this four-level model, two dynamic ways are proposed to achieve the approximately perfect enantio-specific state transfer for symmetric-top chiral molecules.

quant-ph↗

arXiv2021

Quantum Zeno Effect in Heisenberg Picture and Critical Measurement Time

Quantum Zeno effect is conventionally interpreted by the assumption of the wave-packet collapse, in which does not involve the duration of measurement. However, we predict duration $τ_m$ of each measurement will appear in quantum Zeno effect by a dynamical approach. Moreover, there exists a model-free critical measurement time, which quantum Zeno effect does not occur when $τ_m$ takes some special values. In order to give these predictions, we first present a description of quantum Zeno effect in the Heisenberg picture, which is based on the expectation value of an observable and its fluctuation. Then we present a general proof for quantum Zeno effect in the Heisenberg picture, which is independent of the concrete systems. Finally, we calculate the average population and relative fluctuation after $N$ successive measurements in XX model, which agrees with our prediction about the critical measurement time.

quant-ph↗

arXiv2021

Universal scaling of work statistics for quantum quenches

In this paper, we systematically study the work statistics for quantum phase transition. For a quantum system approached by an anisotropic conformal field theory near the critical point, the driving protocols is divided into three different regimes for different quench rates, which reflects the competition between the frozen time and the quench time scale. In each regime, we find universal scaling behaviors in work statistics (after renormalization). It is shown that the critical exponents are determined by the space-time dimension $d$, the dynamical critical exponent $z$, the correlation-length exponent $ν$, and the power-law protocols. These universal scalings in nonequilibrium process may be found in quantum phase transition by measuring the Loschmidt echo or the Ramsey interferometry.

cond-mat.stat-mech↗

arXiv2021

Extrapolating the thermodynamic length with finite-time measurements

The excess work performed in a heat-engine process with given finite operation time τis bounded by the thermodynamic length, which measures the distance during the relaxation along a path in the space of the thermodynamic state. Unfortunately, the thermodynamic length, as a guidance for the heat engine optimization, is beyond the experimental measurement. We propose to measure the thermodynamic length \mathcal{L} through the extrapolation of finite-time measurements \mathcal{L}(τ)=\int_{0}^τ[P_{\mathrm{ex}}(t)]^{1/2}dt via the excess power P_{\mathrm{ex}}(t). The current proposal allows to measure the thermodynamic length for a single control parameter without requiring extra effort to find the optimal control scheme. We illustrate the measurement strategy via examples of the quantum harmonic oscillator with tuning frequency and the classical ideal gas with changing volume.

cond-mat.stat-mech↗

arXiv2020

The uniqueness of the integration factor associated with the exchanged heat in thermodynamics

State functions play important roles in thermodynamics. Different from the process function, such as the exchanged heat $δQ$ and the applied work $δW$, the change of the state function can be expressed as an exact differential. We prove here that, for a generic thermodynamic system, only the inverse of the temperature, namely $1/T$, can serve as the integration factor for the exchanged heat $δQ$. The uniqueness of the integration factor invalidates any attempt to define other state functions associated with the exchanged heat, and in turn, reveals the incorrectness of defining the entransy $E_{vh}=C_VT^2 /2$ as a state function by treating $T$ as an integration factor. We further show the errors in the derivation of entransy by treating the heat capacity $C_V$ as a temperature-independent constant.

cond-mat.stat-mech↗

arXiv2020

Self-consistency of optimizing finite-time Carnot engines with the low-dissipation model

The efficiency at the maximum power (EMP) for finite-time Carnot engines established with the low-dissipation model, relies significantly on the assumption of the inverse proportion scaling of the irreversible entropy generation $ΔS^{(\mathrm{ir})}$ on the operation time $τ$, i.e., $ΔS^{(\mathrm{ir})}\propto1/τ$. The optimal operation time of the finite-time isothermal process for EMP has to be within the valid regime of the inverse proportion scaling. Yet, such consistency was not tested due to the unknown coefficient of the $1/τ$-scaling. In this paper, using a two-level atomic heat engine as an illustration, we reveal that the optimization of the finite-time Carnot engines with the low-dissipation model is self-consistent only in the regime of $η_{\mathrm{C}}\ll1$, where $η_{\mathrm{C}}$ is the Carnot efficiency. In the large-$η_{\mathrm{C}}$ regime, the operation time for EMP obtained with the low-dissipation model is not within the valid regime of the $1/τ$-scaling, and the exact EMP is found to surpass the well-known bound $η_{+}=η_{\mathrm{C}}/(2-η_{\mathrm{C}})$

quant-ph↗

arXiv2020

The hierarchy recurrences in local relaxation

Inside a closed many-body system undergoing the unitary evolution, a small partition of the whole system exhibits a local relaxation. If the total degrees of freedom of the whole system is a large but finite number, such a local relaxation would come across a recurrence after a certain time, namely, the dynamics of the local system suddenly appear random after a well-ordered oscillatory decay process. It is found in this paper, for a collection of $N$ two-level systems (TLSs), the local relaxation of one TLS within has a hierarchy structure hiding in the randomness after such a recurrence: similar recurrences appear in a periodical way, and the later recurrence brings in stronger randomness than the previous one. Both analytical and numerical results that we obtained well explains such hierarchy recurrences: the population of the local TLS (as an open system) diffuses out and regathers back periodically due the finite-size effect of the bath [the remaining $(N-1)$ TLSs]. We also find that the total correlation entropy, which sums up the entropy of all the $N$ TLSs, approximately exhibit a monotonic increase; in contrast, the entropy of each single TLS increases and decreases from time to time, and the entropy of the whole $N$-body system keeps constant during the unitary evolution.

quant-ph↗

arXiv2020

Anomalies of weight-based coherence measure and mixed maximally coherent states

As an analogy of best separable approximation (BSA) in the framework of entanglement theory, here we concentrate on the notion of best incoherent approximation, with application to characterizing and quantifying quantum coherence. From both analytical and numerical perspectives, we have demonstrated that the weight-based coherence measure displays some unusual properties, in sharp contrast to other popular coherence quantifiers. First, by deriving a closed formula for qubit states, we have showed the weight-based coherence measure exhibits a rich (geometrical) structure even in this simplest case. Second, we have identified the existence of mixed maximally coherent states (MMCS) with respect to this coherence measure and discussed the characteristic feature of MMCS in high-dimensional Hilbert spaces. Especially, we present several important families of MMCS by gaining insights from the numerical simulations. Moreover, it is pointed out that some considerations in this work can be generalized to general convex resource theories and a numerical method of improving the computational efficiency for finding the BSA is also discussed.

quant-ph↗

arXiv2019

Quantum coherence fraction

As an analogy of fully entangled fraction in the framework of entanglement theory, we have introduced the notion of quantum coherence fraction $C_{\mathcal{F}}$, which quantifies the closeness between a given state and the set of maximally coherent states. By providing an alternative formulation of the robustness of coherence $C_{\mathcal{R}}$, we have elucidated the relationship between quantum coherence fraction and the normalized version of $C_{\mathcal{R}}$ (i.e., $\overline{C}_{\mathcal{R}}$), where the role of genuinely incoherent operations (GIO) is highlighted. Numerical simulation shows that though as expected $C_{\mathcal{F}}$ is upper bounded by $\overline{C}_{\mathcal{R}}$, $C_{\mathcal{F}}$ constitutes a good approximation to $\overline{C}_{\mathcal{R}}$ especially in low-dimensional Hilbert spaces. Even more intriguingly, we can analytically prove that $C_{\mathcal{F}}$ is exactly equivalent to $\overline{C}_{\mathcal{R}}$ for qubit and qutrit states. Moreover, some intuitive properties and implications of $C_{\mathcal{F}}$ are also indicated.

quant-ph↗

arXiv2018

Objectivity in quantum measurement

The objectivity is a basic requirement for the measurements in the classical world, namely, different observers must reach a consensus on their measurement results, so that they believe that the object exists "objectively" since whoever measures it obtains the same result. We find that this simple requirement of objectivity indeed imposes an important constraint upon quantum measurements, i.e., if two or more observers could reach a consensus on their quantum measurement results, their measurement basis must be orthogonal vector sets. This naturally explains why quantum measurements are based on orthogonal vector basis, which is proposed as one of the axioms in textbooks of quantum mechanics. The role of the macroscopicality of the observers in an objective measurement is discussed, which supports the belief that macroscopicality is a characteristic of classicality.

quant-ph↗

arXiv2018

NV-Metamaterial: Tunable Quantum Hyperbolic Metamaterial Using Nitrogen-Vacancy Centers in Diamond

We show that nitrogen-vacancy (NV) centers in diamond can produce a novel quantum hyperbolic metamaterial. We demonstrate that a hyperbolic dispersion relation in diamond with NV centers can be engineered and dynamically tuned by applying a magnetic field. This quantum hyperbolic metamaterial with a tunable window for the negative refraction allows for the construction of a superlens beyond the diffraction limit. In addition to subwavelength imaging, this NV-metamaterial can be used in spontaneous emission enhancement, heat transport and acoustics, analogue cosmology, and lifetime engineering. Therefore, our proposal interlinks the two hotspot fields, i.e., NV centers and metamaterials.

physics.app-ph↗

arXiv2017

Interpreting quantum coherence through a quantum measurement process

Recently, there has been a renewed interest in the quantification of coherence or other coherence-like concepts within the framework of quantum resource theory. However, rigorously defined or not, the notion of coherence or decoherence has already been used by the community for decades since the advent of quantum theory. Intuitively, the definitions of coherence and decoherence should be the two sides of the same coin. Therefore, a natural question is raised: how can the conventional decoherence processes, such as the von Neumann-Lüders (projective) measurement postulation or partially dephasing channels, fit into the bigger picture of the recently established theoretic framework? Here we show that the state collapse rules of the von Neumann or Lüders-type measurements, as special cases of genuinely incoherent operations (GIO), are consistent with the resource theories of quantum coherence. New hierarchical measures of coherence are proposed for the Lüders-type measurement and their relationship with measurement-dependent discord is addressed. Moreover, utilizing the fixed point theory for $C^\ast$-algebra, we prove that GIO indeed represent a particular type of partially dephasing (phase-damping) channels which have a matrix representation based on the Schur product. By virtue of the Stinespring's dilation theorem, the physical realizations of incoherent operations are investigated in detail and we find that GIO in fact constitute the core of strictly incoherent operations (SIO) and generally incoherent operations (IO) and the unspeakable notion of coherence induced by GIO can be transferred to the theories of speakable coherence by the corresponding permutation or relabeling operators.

quant-ph↗

arXiv2017

Decoherence of Macroscopic Objects from Relativistic Effect

We study how the decoherence of macroscopic objects is induced intrisinically by relativistic effect. With the degree of freedom of center of mass (CM) characterizing the collective quantum state of a macroscopic object (MO), it is found that a MO consisting of N particles can decohere with time scale no more than sqrt(N). Here, the special relativity can induce the coupling of the collective motion mode and the relative motion modes in an order of 1/c2, which intrinsically results in the above minimum decoherence.

quant-ph↗

arXiv2017

Quantum sensing of rotation velocity based on transverse field Ising model

We study a transverse-field Ising model (TFIM) in a rotational reference frame. We find that the effective Hamiltonian of the TFIM of this system depends on the system's rotation velocity. Since the rotation contributes an additional transverse field, the dynamics of TFIM sensitively responses to the rotation velocity at the critical point of quantum phase transition. This observation means that the TFIM can be used for quantum sensing of rotation velocity that can sensitively detect rotation velocity of the total system at the critical point. It is found that the resolution of the quantum sensing scheme we proposed is characterized by the half-width of Loschmidt echo of the dynamics of TFIM when it couples to a quantum system S. And the resolution of this quantum sensing scheme is proportional to the coupling strength δbetween the quantum system S and the TFIM, and to the square root of the number of spins N belonging the TFIM.

quant-ph↗

arXiv2017

Quantum-enhanced microscopy with binary-outcome photon counting

Polarized light microscopy using path-entangled $N$-photon states (i.e., the N00N states) has been demonstrated to surpass the shot-noise limit at very low light illumination. However, the microscopy images suffer from divergence of phase sensitivity, which inevitably reduces the image quality. Here, we show that due to experimental imperfections, such a singularity also takes place in the microscopy that uses twin-Fock states of light for illumination. We propose two schemes to completely eliminate this singularity: (i) locking the phase shift sensed by the beams at the optimal working point, by using a spatially dependent offset phase; (ii) a combination of two binary-outcome photon counting measurements, one with a fixed offset phase and the other without any offset phase. Our observations remain valid for any kind of binary-outcome measurement and may open the way for quantum-enhanced microscopy with high $N$ photon states.

quant-ph↗