Quantum interference at corners

We show that a radiating atom, or molecule, localised at sub-wavelength distances from a corner arising from the intersection of three planar material surfaces, exhibits novel quantum interference effects. The simplest case arises for a corner formed by the intersection of three perfect conductors, all at right angles. This situation is shown here to give rise to super-radiance and sub-radiance effects that are highly sensitive to the dipole moment orientation and position of the radiating atom or molecule in the vicinity of the corner.     

双色场中钾原子的量子干涉现象

采用多态展开方法,对里德堡钾原子与双色场相互作用时诱发的量子干涉效应进行了研究计算,讨论和分析了布居数跃迁过程中的干涉相长及相消的原因.     

Quantum interference and diffraction of parametric down-converted biphotons

We present two-photon diffraction and interference experiments utilizing parametric down-converted photon pairs (biphotons) and a transmission grating. The biphoton exhibits a diffraction-interference pattern equivalent to an effective single particle with half wavelength of the constituent photons.     

Reprint of : Quantum interference in a Cooper pair splitter: The three sites model

New generation of Cooper pair splitters defined on hybrid nanostructures are devices with high tunable coupling parameters. Transport measurements through these devices revealed clear signatures of interference effects and motivated us to introduce a new model, called the 3-sites model. These devices provide an ideal playground to tune the Cooper pair splitting (CPS) efficiency on demand, and displays a rich variety of physical phenomena. In the present work we analyze theoretically the conductance of the 3-sites model in the linear and non-linear regimes and characterize the most representative features that arise by the interplay of the different model parameters. In the linear regime we find that the local processes typically exhibit Fano-shape resonances, while the CPS contribution exhibits Lorentzian-shapes. Remarkably, we find that under certain conditions, the transport is blocked by the presence of a dark state. In the non-linear regime we established a hierarchy of the model parameters to obtain the conditions for optimal efficiency.     

基于Rb原子电磁诱导透明的量子干涉实验研究

报道了基于85RbD2线电磁诱导透明(EIT)的量子干涉现象,发现当一耦合光和探测光之间满足拉曼共振条件时出现电磁诱导透明现象,在某些条件下也观察到电磁诱导吸收(EIA).而当用一束耦合光和一束泵浦光共同作用于5S1/2,F=3→5P3/2,F′=3和5S1/2,F=3→5P3/2,F′=4能级上时,探测光的吸收谱表现出三峰结构,并且峰强弱与两耦合光之间的相对强度有关.     

Quantum interference effect in few-layered transition metal dichalcogenide

Van der Waals layered transition metal dichalcogenides (TMDCs), as atomically flat two-dimensional materials, have been studied extensively in both fundamental science and application fields in recent years. The reduced-dimensional properties of TMDCs not only provide a route for the fabricating of efficient field effect transistors and optoelectronic devices but also suggest the possibility of the devices that utilize quantum coherency. In this work, we characterize the electron transport properties of ReS₂, one of the TMDCs, at both room temperature and low temperature. Of particular note, we measured strong quantum conductance oscillations as a function of the gate voltages and source-drain voltages at reduced temperature, which is evidence of quantum coherent transport. This work unambiguously establishes ReS₂ as a promising candidate for future quantum materials.     

Quantum interference between a single-photon Fock state and a coherent state

We derive analytical expressions for the single mode quantum field state at the individual output ports of a beam splitter when a single-photon Fock state and a coherent state are incident on the input ports. The output states turn out to be a statistical mixture between a displaced Fock state and a coherent state. Consequently we are able to find an analytical expression for the corresponding Wigner function. Because of the generality of our calculations the obtained results are valid for all passive and lossless optical four port devices. We show further how the results can be adapted to the case of the Mach-Zehnder interferometer. In addition we consider the case for which the single-photon Fock state is replaced with a general input state: a coherent input state displaces each general quantum state at the output port of a beam splitter with the displacement parameter being the amplitude of the coherent state.     

Quantifying interference in multipartite quantum systems

The characterization of quantum correlations is crucial to the development of new quantum technologies and to understand how dramatically quantum theory departs from classical physics. Here we systematically study single- and multiparticle interference patterns produced by general two- and three-qubit systems. From this we establish on phenomenological grounds a new type of quantum correlation for these systems, which we name quantum interference, deriving some quantifiers that are given explicitly in terms of the density matrix elements of the complete system. By using these quantifiers, we show that, contrary to our expectations, entanglement is not a required property for a composite quantum system to manifest multiparticle interference.     

An analytical study on absorptive lineshape of a driven N-type open four-level system: Quantum interference effects

An open four-level system of having two pairs of closely spaced levels (N-type configuration) is driven by a single electromagnetic field and tuned resonant with the average frequency of four dipole allowed transitions. Under the Doppler free condition and by using a semiclassical formulation of atom-field interaction for four dipole allowed transitions, we derive the optical Bloch equations for the said four-level system coupled to the driving field. In order to obtain the field induced polarization and hence the absorptive lineshapes, we use the usual perturbation method for getting the approximate analytical solution to the coupled optical Bloch equations for the density matrix elements. Through the off-diagonal complex density matrix elements, we introduce the field dependent phase angles arising out of the quantum interference between the levels participating in dipole allowed transitions. The difference between the field dependent and field independent phases are pointed out. In particular, we investigate the effects of Rabi frequencies and the field dependent phases on the absorptive lineshape. The analytical expressions for the effective linewidths, effective detunings and the induced polarization clearly indicate the role of quantum interference.     

On the environmental decoherence and spin interference in mesoscopic loop structures

Mechanisms of ‘environmental decoherence’ such as surface scattering, Elliot–Yafet process and precession mechanisms, as well as their influence on the spin phase relaxation are considered and compared. It is shown that the ‘spin ballistic’ regime is possible, when the phase relaxation length for the spin part of the wave function (L^(s)) is much greater than the phase relaxation length for the ‘orbital part’ (L^(e)). In the presence of an additional magnetic field, the spin part of the electron's wave function (WF) acquires a phase shift due to additional spin precession about that field. If the structure length L is chosen to be L^(s)>L>L^(e), it is possible to ‘wash out’ the quantum interference related to the phase coherence of the ‘orbital part’ of the WF, retaining at the same time that related to the phase coherence of the spin part and, hence, to reveal corresponding conductance oscillations.     

Quantum interference of charged identical particles

We present the results of a computer simulation study of charged-particle interferometry, combining features of both the Aharonov-Bohm and Hanbury Brown-Twiss experiment. In contrast to a previous theoretical analysis of this experiment, we find that the Aharonov-Bohm effect is also present in the cross-correlated two-particle intensity. A simple, time-independent scattering theory that leads to conclusions that are in concert with the simulation data is given.     

Time-dependent transport through a quantum dot with the over-dot (bridge) additional tunneling channel

The time-dependent electron transport through a quantum dot with the additional over-dot (bridge) tunneling channel within the evolution operator technique has been studied. The microwave field applied to the leads and quantum dot has been considered and influence of the time-dependent shift of corresponding energy levels on the quantum dot charge and current flowing in the system, its time-averaged values and derivatives of the average current with respect to the gate and source–drain bias voltages have been investigated. The influence of the over-dot tunneling channel on the photon-assisted tunneling has been also studied.     

Quantum heat switch with multiple qubits

We further elaborate on the device proposed by Karimi et al. [15], in which coupled superconducting qubits can play the role of a quantum heat switch. In the present paper we analyze the performances of the switch if the number of qubits increases considering in details the cases of three and four qubits. To this aim we study the effect of the number of qubits on the transmitted power between baths. As the number of qubits increases, the transmitted power between baths increases as well.     

Coherent control of quantum entropy via quantum interference in a four-level N-type atomic system

The time evaluation of quantum entropy in a four-level N-type atomic system is theoretically investigated. Quantum entanglement of the atom and its spontaneous emission fields is then discussed via quantum entropy. It is found that the degree of entanglement can be increased by the quantum interference induced by spontaneous emission. The phase dependence of the atom-field entanglement is also presented.     

Quantum point contacts as heat engines

The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely.     

Quantum analysis on the four-photon interference

We present a theory for quantum interference of four photons generated by spontaneous parametric down-conversion. Detailed investigation of the dependence of fourfold coincidence count rate on time delay between the incident and the reflective pump laser pulses is carried out. Gaussian type dependence is found, and good agreement between our theoretical results and experimental data reported in the literature is achieved.     

Quantum analysis on the four-photon interference

We present a theory for quantum interference of four photons generated by spontaneous parametric downconversion. Detailed investigation of the dependence of fourfold coincidence count rate on time delay between the incident and the reflective pump laser pulses is carried out. Gaussian type dependence is found, and good agreement between our theoretical results and experimental data reported in the literature is achieved.