Quantum Electrodynamics Cavity Research Articles

Study different quantum teleportation amounts by solving Lindblad master equation

A realizable model based on the interaction between an excited two-level atom and a radiation field inside two quantum electrodynamics cavities is proposed. It consists of sending the excited atom through two serial cavities which contain the radiation field. Thus, the Lindblad master equations which describe the evolution of the reduced density matrix regarding the radiation field generated from the excited atom inside the cavities are solved in Markovian and non-Markovian regimes. Thereby, the rate of entanglement inherent in the total field-field system is evaluated using various witnesses by calculating analytically the concurrence and quantum discord, where we illustrate quantitatively the advantage of using an initial EPR and NOON states in the presence of radiation field losses. As an application, a scheme of quantum teleportation using two partial entangled channels is investigated. Finally, a comparative study between fidelity and the different levels of entanglement of the teleported state in the two regimes is also given.

On the interaction between a time-dependent field and a two-level atom

In this paper, we study the interaction between the time-dependent field and a two-level atom with one mode electromagnetic field. We consider that the field of photons is assumed to be coupled with modulated coupling parameter which depends explicitly on time. It is shown that the considered model can be reduced to a well-known form of the time-dependent generalized Jaynes–Cummings model. Under special initial conditions, in which the atom and the field are prepared in the excited and the coherent states, respectively, the explicit time evolution of the wave function of the entire system is analytically obtained. Our proposal has many advantages over the previous optical schemes and can be realized in several multiple experiments, such as trapped ions and quantum electrodynamics cavity. The influence of the time-dependent field parameter on the collapses-revivals, the normal squeezing of the radiation, the anti-bunching of photons and the entanglement phenomena for the considered atomic system is examined. The linear entropy, the von Neumann entropy are used to quantify entanglement in the quantum systems. We noticed that these phenomena are affected by the existence of both the time-dependent coupling field and detuning parameters.

Multipartite quantum correlations among atoms in QED cavities

We study the nonlocality dynamics for two models of atoms in cavity quantum electrodynamics (QED); the first model contains atoms in a single cavity undergoing nearest-neighbor interactions with no initial correlation, and the second contains atoms confined in n different and noninteracting cavities, all of which were initially prepared in a maximally correlated state of n qubits corresponding to the atomic degrees of freedom. The nonlocality evolution of the states in the second model shows that the corresponding maximal violation of a multipartite Bell inequality exhibits revivals at precise times, defining, nonlocality sudden deaths and nonlocality sudden rebirths, in analogy with entanglement. These quantum correlations are provided analytically for the second model to make the study more thorough. Differences in the first model regarding whether the array of atoms inside the cavity is arranged in a periodic or open fashion are crucial to the generation or redistribution of quantum correlations. This contribution paves the way to using the nonlocality multipartite correlation measure for describing the collective complex behavior displayed by slightly interacting cavity QED arrays.

Absorption in quantum electrodynamic cavities in terms of a quantum jump operator

We describe the absorption by the walls of a quantum electrodynamics cavity as a process during which the elementary excitations (photons) of an internal mode of the cavity exit by tunneling through the cavity walls. We estimate by classical methods the survival time of a photon inside the cavity and the quality factor of its mirrors.

Quantum computer with atomic logical qubits encoded on macroscopic three-level systems in common quantum electrodynamic cavity

We propose an effective realization of the universal set of elementary quantum gates in solid state quantum computer based on macroscopic (or mesoscopic) resonance systems — multiatomic coherent ensembles, squids or quantum dots in quantum electrodynamic cavity. We exploit an encoding of logical qubits by the pairs of the macroscopic two- or three-level atoms that is working in a Hilbert subspace of all states inherent to these atomic systems. In this subspace, logical single qubit gates are realized by the controlled reversible transfer of single atomic excitation in the pair via the exchange of virtual photons and by the frequency shift of one of the atomic ensembles in a pair. In the case of two-level systems, the logical two-qubit gates are performed by the controlling of Lamb shift magnitude in one atomic ensemble, allowing/blocking the excitation transfer in a pair, respectively, that is controlled by the third atomic system of another pair. When using three-level systems, we describe the NOT-gate in the atomic pair controlled by the transfer of working atomic excitation to the additional third level caused by direct impact of the control pair excitation. Finally, we discuss advantages of the proposed physical system for accelerated computation of some useful quantum gates.

Photon echo quantum random access memory integration in a quantum computer

We have analysed an efficient integration of multi-qubit echo quantum memory (QM) into the quantum computer scheme based on squids, quantum dots or atomic resonant ensembles in a quantum electrodynamics cavity. Here, one atomic ensemble with controllable inhomogeneous broadening is used for the QM node and other nodes characterized by the homogeneously broadened resonant line are used for processing. We have found the optimal conditions for the efficient integration of the multi-qubit QM modified for the analysed scheme, and we have determined the self-temporal modes providing a perfect reversible transfer of the photon qubits between the QM node and arbitrary processing nodes. The obtained results open the way for realization of a full-scale solid state quantum computing based on the efficient multi-qubit QM.

Quantum computers on multiatomic ensembles in quantum electrodynamic cavity

Schemes for the construction of quantum computers on multiatomic ensembles in quantum electrodynamic cavity are considered. With that, both encoding of physical qubits on each separate multiatomic ensemble and logical encoding of qubits on the pairs of ensembles are introduced. Possible constructions of swapping (SWAP, \(\sqrt {SWAP} \)) and controlled swapping gates (CSWAP) are analyzed. Mechanism of collective blockade and dynamical elimination procedure are proposed for realization of these gates. The comparison of the scheme solutions is carried out for the construction of quantum computer at using of physical and logical qubits.

Solid state multi-ensemble quantum computer in cavity quantum electrodynamics model

The first realization of solid state quantum computer was demonstrated recently by using artificial atoms — transmons in superconducting resonator. Here, we propose a novel quantum computer based on quantum electrodynamic cavity coupling many quantum nodes of controlled atomic ensembles. The quantum computer contains quantum memory and processing nodes. For the first time, we find the optimal practically attainable parameters of the atoms and optical scheme of the computer for realization of the multimode quantum memory for the photonic qubits with efficiency close to 100%. Then we reveal self modes for reversible transfer of the qubits between the quantum memory node and the processing nodes. Also, we find a realization of iSWAP gate via direct coupling of two processing nodes with an operation rate accelerated proportionally to the number of atoms in the nodes. Collective dynamic and static blockade mechanisms are proposed for realization of $\sqrt {iSWAP} $ quantum gate in multi atomic ensembles. A large number of the two-qubit gates can be simultaneously realized that opens a possibility for parallel quantum processing in the proposed quantum computer.

Quantum-information transfer with nitrogen-vacancy centers coupled to a whispering-gallery microresonator

We propose an efficient scheme for the realization of quantum information transfer and entanglement with nitrogen-vacancy (NV) centers coupled to a high-Q whispering-gallery mode (WGM) microresonator. We show that, based on the effective dipole-dipole interaction between the NV centers mediated by the WGM, quantum information can be transferred between the NV centers through Raman transitions combined with laser fields. This protocol may open up promising possibilities for quantum communications with the solid state cavity QED system.

Fast and robust two- and three-qubit swapping gates on multi-atomic ensembles in quantum electrodynamic cavity

Creation of quantum computer is outstanding fundamental and practical problem. The quantum computer could be used for execution of very complicated tasks which are not solvable with the classical computers. The first prototype of solid state quantum computer was created in 2009 with superconducting qubits. However, it suffers from the decoherent processes and it is desirable to find more practical encoding of qubits with long-lived coherence. It could be single impurity or vacancy centers in solids, but their interaction with electromagnetic radiation is rather weak. So, here, ensembles of atoms were proposed for the qubit encoding by using the dipole blockade mechanism in order to turn multilevel systems in two level ones. But dipole-dipole based blockade introduces an additional decoherence that limits its practical significance. Recently, the collective blockade mechanism has been proposed for the system of three-level atoms by using the different frequency shifts for the Raman transitions between the collective atomic states characterized by a different number of the excited atoms. Here, we propose two qubit gate by using another collective blockade mechanism in the system of two level atoms based on exchange interaction via the virtual photons between the multi-atomic ensembles in the resonator. Also we demonstrate the possibility of three qubit gate (Controlled SWAP gate) using a suppression of the swap-process between two multi-atomic ensembles due to dynamical shift of the atomic levels controlled by the states of photon encoded qubit.

Bose–Hubbard dynamics of polaritons in a chain of circuit quantum electrodynamics cavities

We investigate a chain of superconducting stripline resonators, each interacting with a transmon qubit, that are capacitively coupled in a row. We show that the dynamics of this system can be described by a Bose–Hubbard Hamiltonian with attractive interactions for polaritons, superpositions of photons and qubit excitations. This setup, we envisage, is one of the first platforms where all the technological components that are needed to experimentally study chains of strongly interacting polaritons have already been realized. By driving the first stripline resonator with a microwave source and detecting the output field of the last stripline resonator, one can spectroscopically probe the properties of the system in the driven dissipative regime. We calculate the stationary polariton density and density–density correlations g(2) for the last cavity, which can be measured via the output field. Our results display a transition from a coherent to a quantum field as the ratio of on-site interactions to driving strength is increased.

Modelling of quantum networks of feedback QED systems in interacting Fock space

The present article is concerned with the study of quantum electrodynamics (QED) in interacting Fock space and a generalised approach of modelling quantum feedback systems of the optical QED cavities. The dynamical behaviour and the state space representation in stochastic field of the optical QED system provide the basis for developing quantum feedback QED control system. This study is also motivated by the design of quantum networks of any number of optical QED baths connected in parallel. Nyquist stability of the feedback control system in the interacting Fock space using two-mode beam splitter device at the input and a single-mode fractional beam splitter device at the output of the cavity has been analysed. The degree of stability of the quantum feedback control system of the cavity QED is studied by measuring gain margin and phase margin of the system in terms of parameters of the beam splitter.

Mean-field dynamics of a Bose Josephson junction in an optical cavity

We study the mean-field dynamics of a Bose Josephson junction which is dispersively coupled to a single mode of a high-finesse optical cavity. An effective classical Hamiltonian for the Bose Josephson junction is derived, and its dynamics is studied from the perspective of a phase portrait. It is shown that the strong condensate-field interplay does alter the dynamics of the Bose Josephson junction drastically. The possibility of coherent manipulating and in situ observation of the dynamics of the Bose Josephson junction is discussed. Cavity quantum electrodynamics cavity QED has now grown into a paradigm in the study of the matter-field interaction. To tailor the atom-field coupling effectively, a high degree of control over the center-of-mass motion of the atoms is essential. Although previous works have focused on the few-atom level 1, recently, a great step was made as two groups succeeded independently in coupling a BoseEinstein condensate to a single-cavity mode 2,3. That is, a single-cavity mode dressed condensate has been achieved. This opens up a new regime in both the fields of cavity QED and ultracold atom physics. In the condensate, all the atoms occupy the same motional mode and couple identically to the cavity mode, thus realizing the Dicke model 4 in a broad sense. As shown by these experiments, the condensate is quite robust; it would not be destroyed by its interaction with the cavity mode in the time scale of the experiments. In this paper, we investigate the mean-field dynamics of a Bose Josephson junction BJJ5, which is coupled to a driven cavity mode. This extends our previous work to the many-atom case 6. The system may be constructed by splitting a Bose-Einstein condensate, which is already coupled to a single-cavity mode, into two weakly linked condensates, as can be done in a variety of ways 7‐11. We restrict ourselves to the large-detuning and low-excitation limit, so that atomic spontaneous emission can be neglected. In this limit, the effect of the strong coupling between the atoms and the field, seen by the field, is to shift the cavity resonance frequency and hence modify the field intensity. Unlike the single-condensate case, we now have two, which may couple with different strengths to the cavity mode because of the position dependence of the atom-field coupling. Consequently, the field dynamics couples to the tunneling dynamics of the BJJ and vice versa. It is the very interplay between the two sides that we are interested in. The interplay is made possible by the greatly enhanced atom-field coupling in a microcavity, which is unique in the context of cavity QED. In the usual optical traps and optical lattices, the interaction between the atoms and the light field is one way in the sense that the light field affects the motion of the atoms effectively, while the atoms have little back-action on the light field—the laser intensity is almost the same with or without the presence of the atoms. We would like to stress that, although there had already been some experimental investigations on this subject and phenomena such as dispersive optical bistability were observed 12,13, all of them dealt with thermally cold atoms. However, here, the long-range coherence of the condensates will surely make a difference. The Hamiltonian of the system consists of three parts: H = Ha + Hf + Hint. 1 Ha is the canonical Bose-Josephson-junction Hamiltonian in the two-mode approximation =1 throughout,

Cooper-pair-box qubits in a quantum electrodynamic cavity

We study the quantum dynamics of Cooper-pair-box qubits in a quantum electrodynamic cavity. We show the existence of Rabi oscillations for both single- and multi-photon processes and propose a quantum computing scheme.