We examine a quantum absorption refrigerator that comprises three qubits, each of which is connected with a separate spin-star environment. The refrigerator exhibits the feature of transient cooling, i.e., lowering of the temperature of the first qubit in sufficiently small timescales. Since the spin-star environment is inherently non-Markovian in nature, steady-state cooling may or may not be achieved. A key advantage of our model is that the symmetries of the Hamiltonian enable a solution of the reduced density matrices of the refrigerator qubits, even in the presence of a large number ( 50) of environmental spins. We derive the condition for autonomous refrigeration and analyze how the optimal cold qubit temperature scales with the number of bath qubits. We find a power law scaling towards a constant asymptotic value. We also find the scaling of the minimum time required for cooling as a function of the number of bath spins. Further, we scrutinize the heat currents associated with each of the three qubits.
The equations of time-dependent density functional theory are derived, via the expression for a quantum weak value, from ring polymer self-consistent field theory using a mathematical correspondence between time and imaginary time. The imaginary time path integral formalism of Feynman, in which inverse temperature is seen to be a Wick rotation of time, allows one to write the equilibrium partition function of a quantum system in a form mathematically isomorphic with the path integral expression for the dynamics. Therefore the self-consistent field theory equations which are solutions to the equilibrium partition function are Wick rotated back into a set of dynamic equations, which are shown to give an expression for a quantum weak value of the one-particle density. Remarkably, weak values emerge naturally here without being postulated, as an intermediate step before recovering the standard expression for the density. The weak value expression in turn leads to the equations of time-dependent density functional theory. This first-principles derivation does not use the theorems of density functional theory, which are instead applied to guarantee equivalence with standard quantum mechanics. An expression for finite-temperature dynamics is also given, which shows that a ring polymer model for quantum particles holds for time-dependent systems as well as equilibrium situations. Issues arising in time-dependent density functional theory, such as causality, initial state dependence, and v-representability, are discussed in the context of the ring polymer derivation.
We propose a distributed quantum dense coding protocol that uses a control system to superpose two dense coding processes, allowing us to simultaneously and coherently encode and non-classically route the sender's single-qubit system to two receiver labs. We find that dense coding with coherently controlled encoding and routing performs better than the standard dense coding protocol in both global and one-way local decoding strategies employed by receiver labs in weak entanglement regimes and with noisy mixed states. We extend our protocol to an arbitrary number of receivers and analyse its performance under a global decoding strategy.
Exceptional points (EPs) are remarkable spectral degeneracies in a non-Hermitian system's parameter space, where both eigenvalues and eigenstates coalesce. Here, we show that in non-Hermitian molecular chiral systems the position of EPs in the parameter space is enantiomer-specific. First, we show that encircling the EP of one enantiomer drives robust topological population transfer in the chiral molecule while its mirror twin remains unaffected, offering a route for selective chiral control. Second, we reveal how resonant excitation of EPs in chiral molecules can amplify weak chiral effects, offering an alternative approach to the enhancement of chiral interactions. Third, we demonstrate that a twisted chiral fiber immersed in a liquid solution of chiral molecules exhibits topologically different behavior depending on the solution's enantiomeric excess, offering a topological approach to the detection of molecular chirality. Our results combine high enantiosensitivity with topological robustness in chiral discrimination and control, paving the way for alternative approaches in the exploration of non-Hermitian and chiral phenomena.
Optically-levitated dielectric objects are promising for precision force, acceleration, torque, and rotation sensing due to their extreme environmental decoupling. While many levitated opto-mechanics experiments employ spherical objects, for some applications non-spherical geometries offer advantages. For example, rod-shaped or dumbbell shaped particles have been demonstrated for torque and rotation sensing and high aspect ratio plate-like particles can exhibit reduced photon recoil heating and may be useful for high-frequency gravitational wave detection or as high bandwidth accelerometers. To achieve optimal sensitivity, cooling, and quantum control in these systems, it is beneficial to achieve optimal displacement detection using scattered light. We describe and numerically implement a method based on Fisher information that is applicable to suspended particles of arbitrary geometry. We demonstrate the agreement between our method and prior methods employed for spherical particles, both in the Rayleigh and Lorentz-Mie regimes. As practical examples we analyze the optical detection limits of an optically-levitated high-aspect-ratio disc-like dielectric object and a rod-shaped object for configurations recently realized in experimental work.
Many current quantum error correcting codes that achieve full fault-tolerance suffer from having low ratios of logical to physical qubits and significant overhead. This makes them difficult to implement on current noisy intermediate-scale quantum (NISQ) computers and results in the inability to perform quantum algorithms at useful scales with near-term quantum processors. Due to this, calculations are generally done without encoding. We propose a middle ground between these two approaches: constructions in the [[n,n-2,2]] quantum error detecting code that can detect any error from a single faulty gate by measuring the stabilizer generators of the code and additional ancillas at the end of the computation. This achieves what we call weak fault-tolerance. As we show, this demonstrates a significant improvement over no error correction for low enough physical error probabilities and requires much less overhead than codes that achieve full fault-tolerance. We give constructions for a set of gates that achieve universal quantum computation in this error detecting code, while satisfying weak fault-tolerance up to analog imprecision on the physical rotation gate.
Elegant Bell inequality is well known for its distinctive property, being maximally violated by maximal entanglement, mutually unbiased bases, and symmetric informationally complete positive operator-valued measure elements. Despite its significance in quantum information theory demonstrated based on its unique violation feature, it remains the only known one with the characteristic. We present a method to construct Bell inequalities with violation feature analogous to elegant Bell inequality in higher local dimensions from a simple, analytic quantum bound. A Bell inequality with the generalized violation feature is derived in three dimension for the first time. It exhibits larger violation than existing Bell inequalities of similar classes, including the original elegant Bell inequality, while requiring arguably small number of measurements.
In spite of its applicability to relativistic incident particles it is well known that the Bethe stopping power theory limited to nonrelativistic target elements with eigenstates isfying the Schro ̈dinger equation for many-electron atom This limitation arises mainly from the derivation of the orig nal Bethe theory, which has applied the various nonrela istic sum rules~the Bethe and TRK sum rules ! @1#. For heavy elements, one would expect a nontrivial correction to Bethe theory due to the fast motion of the inner shell el trons. This problem was first pointed out by Fano in 1964 a review of the outstanding unsolved problems in stopp power theory which existed at that time @2#. Since then, to the knowledge of the author, not much effort has been voted to the study of this problem until recently @3–5#. As also pointed out by Fano in the same review @2#, the difficulty in solving this problem lies right in the possible gene alization of the various sum rules to the relativistic doma Indeed, the relativistic generalization of various atom sum rules has been an intriguing problem over the pas years since the first work on the generalization of the T sum rule@6#. It has been studied extensively in the literatu using both the single-particle and many-particle ~fieldtheoretic! approaches@7–11#. In a previous attempt, we hav used a semirelativistic single-particle approach to obtain leading relativistic correction terms to the Bethe sum rule @9# and applied the results to derive corrections to the Be stopping power theory for heavy target atoms @3#. Unfortunately, it was pointed out later @10# that in most of these previous works based on the same approach @6,7,9,11#, there exists an inconsistency in that the transformation of the erator was not included in the Foldy-Wouthuysen transf mation performed, which leads to the semirelativistic corr tion terms for the sum rules. Very recently @12#, this error has been corrected and it was found that while the prev corrections to the TRK sum rule were not affected by t error, those for the Bethe sum rule have to be modified. It is the purpose of this paper to apply these latest c rected results for the semirelativistic sum rules to amend previous work published in the correction to the Bethe st ping power theory@3#. As before, we shall limit ourselves t the single-particle case and apply the results to a real a by adopting the independent-particle, local-potential desc tion. Though this seems to be an oversimplified picture does have some success in the literature in the analys x-ray scattering data using the TRK sum rule @13#. In any case, our preliminary attempt will at least give a first es
Measurements are reported of the evolution of bioconvective patterns in shallow, dense cultures of microorganisms subjected to varying gravity. Various statistical properties of this random, quasi-two-dimensional structure have been found: Aboav's law is obeyed, the average vertex angles follow predictions for regular polygons, and the area of a pattern varies linearly with its number of sides. As gravity varies between 1 g and 1.8g (g = 9.8 m s-1), these statistical properties continue to hold despite a tripling of the number of polygons and a reduced average polygon dimension by a third. This work compares with experiments on soap foams, Langmuir monolayer foams, metal grains, and simulations.
On admet en general que le refroidissement par laser d'un cristal ionique est qualitativement le meme que celui d'un ion isole. On montre que cette hypothese est violee dans des experiences sur des pieges de Paul, par suite du micromouvement des ions. On demontre qu'une instabilite inattendue d'amortissement par laser, qui induit une transition ordre-chaos explique pourquoi les cristaux ioniques dans des pieges de Paul sont limites a moins de 100 ions
Photon-counting experiments have been conducted to test the conjecture that at sufficiently high laser irradiance, atomic inner-shell excitations can be induced by laser-driven outer-shell oscillations. Using KrF light at an irradiance \ensuremath{\approxeq}3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ W/${\mathrm{cm}}^{2}$ on low-density noble-gas targets, we detect no prompt photons which are characteristic of inner-shell processes.
A distorted-wave calculation for electron-impact 1 {sup 1}S--2{sup 1}P excitation in helium is performed using Slater's concept of transition state'' for obtaining the distortion potential of the projectile electron. Results for differential cross sections, angular momentum {l angle}{ital L}{sub {perpendicular}}{r angle}, and alignment angle {gamma} are obtained. Present results show good agreement with the available experimental data in the energy range from 60 to 200 eV.
Discussion de l'hydrodynamique lineaire et non lineaire des automates reseau-gaz a 2 dimensions. En plus des modes sonores et de cisaillement, il y a 3 nouveaux modes hydrodynamiques. Il y a un couplage non lineaire entre 2 classes de modes et, alors que les nouvelles densites conservees convergent par suite de la densite de moments, on met en evidence des termes qui dependent uniquement des nouveau modes
La diffusion d'une classe de champs electromagnetiques partiellement coherents par un modele de milieu dont la susceptibilite dielectrique fluctue dans l'espace et dans le temps, est consideree avec la precision de l'approximation du 1er ordre de Born. Si le champ incident a une polarisation rectiligne avec un spectre a profil gaussien, le spectre diffuse peut etre approximativement gaussien
We report the first quantitative theoretical and experimental studies of frequency shifts of nuclear-magnetic-resonance (NMR) lines of noble-gas atoms and the corresponding frequency shifts of electron-paramagnetic-resonance (EPR) lines of alkali-metal atoms in mixtures of nuclear spin-polarized noble gases and vapors of spin-polarized alkali-metal atoms. The shifts are primarily due to the Fermi-contact hyperfine interaction. For the heavier noble gases there can be relatively large (\ensuremath{\approxeq}10%) contributions to the shifts from van der Waals molecules. The NMR frequencies of polarized $^{83}\mathrm{Kr}$ and $^{129}\mathrm{Xe}$ were measured in a vapor of spin-polarized alkali-metal atoms oriented parallel and antiparallel to the external magnetic field. The shift in the EPR frequency of the alkali-metal vapor due to the polarized noble-gas nuclei was measured simultaneously, thus providing a measurement of the absolute noble-gas nuclear polarization. The frequency shifts can be used as a convenient way to measure the absolute nuclear spin polarization of noble gases.
The absolute two-photon excitation cross section for the H/sub 2/ E,F /sup 1/..sigma../sub g/ (v' = 6)left-arrowX/sup 1/..sigma../sub g/ (v'' = 0) Q(1) transition at 193 nm has been measured by observing the E,F /sup 1/..sigma../sub g//sup +/ (v' = 6)->B /sup 1/..sigma../sub u//sup +/ (v'' = 0) fluorescence at /similar to/750 nm. The measured integrated two-photon excitation cross section, (2.0 +- 0.9) x 10/sup -36/ cm/sup 4/, is in good agreement with the theoretical value of 2.8 x 10/sup -36/ cm/sup 4/, which is obtained from previously published calculations (Huo and Jaffe, Chem. Phys. Lett. 101, 463 (1983)). The absolute cross section for photoabsorption by the E,F state at 355 and 193 nm was also measured by monitoring the depletion of the 750-nm fluorescence caused by a second laser. The measured cross sections for photoabsorption by the E,F (v = 6) state are (9.7 +- 2.4) x 10/sup -18/ cm/sup 2/ at 355 nm and (6.4 +- 1.3) x 10/sup -18/ cm/sup 2/ at 193 nm. Comparison with theoretical estimates (Cohn, J. Chem. Phys. 57, 2456 (1972)) of the direct photoionization cross section of this state (8.5 x 10/sup -18/ cm/sup 2/ at 355 nm and 3.2 x 10/supmore » -18/ cm/sup 2/ at 193 nm) suggests that other processes may contribute to the photoabsorption.« less
Information-theory techniques are employed in order to deal with the dynamics of nonlinear quantal Hamiltonians. Some interesting new results are obtained that tend to dispel some widely shared notions concerning the Hamiltonian approach to quantal dissipation effects.
Time-resolved extreme-UV emission from sixteen 3p-3s transitions, some of the type in which lasing has been demonstrated in heavier elements, is measured for neonlike Ar(8+) and Cl(7+). These observations are made on a hydrogen theta-pinch plasma with a 5 pct admixture of argon or freon (for Cl). Fourteen 3d-3p spectral lines are also detected. The measured intensities are compared to theoretical predictions. There is no evidence of anomalously intense lines originating on 2p5 3p J = 2 upper levels compared to J = 0, as observed in gain experiments.
