Abstract We investigate the quantum interference effect of single photon transfer in a two-atom cavity system caused by the excitation phase. In the proposed system, the two identical atoms are firstly put into a timed state by an external single photon field. During the excitation, the atoms grasp different phases which depend on the spatial position of the atoms. Due to the strong resonant interaction between the atoms and optical cavity mode, the absorbed input photon can be efficiently transferred from the atoms to the cavity mode. We show that photon transfer is sensitive to the quantum interference caused by the excitation phases of atoms. The atomic positions can also determine the coupling constants between the atoms and cavity mode as well as the interatomic dipole–dipole interaction which causes additional interference effects on the quantum transfer. Based on the characteristics of the excitation phase, we find that it is a feasible scheme to generate a long-lived dark state and it could be useful for storage and manipulation of single photon fields by controlling the excitation phase.
Abstract We investigate the quantum interference effect of single photon transfer in a two-atom cavity system caused by the excitation phase. In the proposed system, the two identical atoms are firstly put into a timed state by an external single photon field. During the excitation, the atoms grasp different phases which depend on the spatial position of the atoms. Due to the strong resonant interaction between the atoms and optical cavity mode, the absorbed input photon can be efficiently transferred from the atoms to the cavity mode. We show that photon transfer is sensitive to the quantum interference caused by the excitation phases of atoms. The atomic positions can also determine the coupling constants between the atoms and cavity mode as well as the interatomic dipole–dipole interaction which causes additional interference effects on the quantum transfer. Based on the characteristics of the excitation phase, we find that it is a feasible scheme to generate a long-lived dark state and it could be useful for storage and manipulation of single photon fields by controlling the excitation phase.
The transmission spectrum of a two-atom timed Dicke state is investigated in an open optical cavity. In the proposed system, two identical atoms are excited by an external single photon field. In this process, the excited atoms grasp different excitation phases for their different spatial positions. For identical coupling strength of atoms and cavity, the excitation phases get coupled via cavity and vacuum fields, and they finally induce cosine-type quantum interference on the two splitting peaks of the spectrum. However, when one of the atoms is decoupled with the cavity, the excitation phases cannot get coupled directly via the cavity but must be mediated by the vacuum fields, which leads to opposite quantum interference effects on the two splitting peaks. In addition, we find that the real and virtual vacuum-mediated excitation phase couplings generate different quantum interferences. The real vacuum-meditated coupling induces sine-type quantum interference, while it becomes cosine-type for the virtual vacuum-mediated coupling. Our study clarifies the mechanism of quantum interference in the two-atom timed Dicke state and provides a feasible scheme for investigating the effect of vacuum-mediated excitation phase coupling.
The cause of decoherence in a quantum system can be traced back to the interaction with the environment. As it has been pointed out by Dicke, in a system of N two-level atoms, where each of the atoms is individually dipole coupled to the environment, there are collective, subradiant states, that have no dipole coupling to photon modes, and therefore, they are expected to decay slower. This property also implies that these type of states decohere slower. We propose a scheme which will create such states. First, the two-level atoms are placed in a strongly detuned cavity and one of the atoms, called the control atom is excited. The time evolution of the coupled atom-cavity system leads to an appropriately entangled state of the atoms. By the aid of a suitable single-atom phase transformation, it is possible to drive the atomic state into the subradiant, i.e., decoherence-free subspace. Up to a certain average number of photons, the result is independent of the state of the cavity. The analysis of the conditions shows that this scheme is feasible with present day techniques achieved in atom-cavity interaction experiments.
The dark-state effect, caused by destructive interference, not only is an important fundamental research topic in atomic physics and quantum optics, but also has wide potential application in quantum physics and quantum information science. Using the arrowhead-matrix method, here we study the dark-state effect in a coupled cavity-Rydberg-atom system, in which N Rydberg atoms with the dipole-dipole interactions are coupled to a single-mode cavity field. We obtain the numbers and form of the dark states in certain excitation-number subspaces for the two-, three-, and four-atom cases, as well as in the single-excitation subspace for a general N-atom case. We also suggest to characterize the dark states by inspecting the populations of some specific quantum states, which can be detected in experiments. Furthermore, we analyze the dark-state effect in a realistic case, where both the atomic dipole-dipole interaction strengths and the atom-cavity-field coupling strengths depend on the position of the atoms. Our findings pave the way for studying dark-state physics and applications in the cavity-Rydberg-atom platform.
We propose and analyze a scheme for controlling coherent photon transmission and reflection in a cavity-quantum-electrodynamics (CQED) system consisting of an optical resonator coupled with three-level atoms coherently prepared by a control laser from free space. When the control laser is off and the cavity is excited by two identical light fields from two ends of the cavity, the two input light fields can be completely absorbed by the CQED system and the light energy is converted into the excitation of the polariton states, but no light can escape from the cavity. Two distinct cases of controlling the perfect photon absorption are analyzed: (a) when the control laser is tuned to the atomic resonance and creates electromagnetically induced transparency, the perfect photon absorption is suppressed and the input light fields are nearly completely transmitted through the cavity; (b) when the control laser is tuned to the polariton state resonance and inhibits the polariton state excitation, the perfect photon absorption is again suppressed and the input light fields are nearly completely reflected from the cavity. Thus, the CQED system can act as a perfect absorber or near-perfect transmitter and/or reflector by simply turning the control laser off or on. Such interference control of the coherent photon-atom interaction in the CQED system should be useful for a variety of applications in optical logical devices.
We propose to couple single atomic qubits to photons incident on a cavity containing an atomic ensemble of a different species that mediates the coupling via Rydberg interactions. Subject to a classical field and the cavity field, the ensemble forms a collective dark state which is resonant with the input photon, while excitation of a qubit atom leads to a secondary ``dark'' state that splits the cavity resonance. The two different dark-state mechanisms yield zero and $\ensuremath{\pi}$ reflection phase shifts and can be used to implement quantum gates between atomic and optical qubits.
Rapid advances in quantum technology have made possible the control of quantum states of elementary material quantum systems, such as atoms or molecules, and of the electromagnetic radiation field resulting from spontaneous photon emission of their unstable excited states to such a level of precision that subtle quantum electrodynamical phenomena have become observable experimentally. Recent developments in the area of quantum information processing demonstrate that characteristic quantum electrodynamical effects can even be exploited for practical purposes provided the relevant electromagnetic field modes are controlled by appropriate cavities. A central problem in this context is the realization of an ideal transfer of quantum information between a state of a material quantum system and a quantum state of the electromagnetic radiation field which contains a small number or even a single photon only. Despite much recent work in cavity quantum electrodynamics, which has explored this problem successfully in cases in which the number of accessible electromagnetic field modes is strongly restricted by a cavity, currently still much less is known about ideal quantum state transfer between matter and few-photon quantum states of the electromagnetic field in the extreme opposite case of free space. In this contribution we review recent work which explores characteristic quantum electrodynamical phenomena governing the interaction of a material quantum system with the electromagnetic field in extreme many-mode cases which are close to cavity-free situations. For this purpose the simplest possible quantum electrodynamical situation, namely the interaction of a single material two-level system with the wave packet of a single optical photon, is investigated in free space and in situations in which a large cavity modifies the mode structure of the electromagnetic field modes. It is demonstrated that perfect excitation of an atom by a properly shaped single-photon wave packet is possible even in free space. In particular, it is demonstrated that perfect excitation of an atom can be achieved by a single optical photon which is prepared initially in an appropriate superposition of plane-wave modes, provided this photon is focused subsequently onto the absorbing atom by a parabolic cavity.