Classical Laser Field Research Articles

Quantum interference induced photon blockade in a coupled single quantum dot-cavity system.

We propose an experimental scheme to implement a strong photon blockade with a single quantum dot coupled to a nanocavity. The photon blockade effect can be tremendously enhanced by driving the cavity and the quantum dot simultaneously with two classical laser fields. This enhancement of photon blockade is ascribed to the quantum interference effect to avoid two-photon excitation of the cavity field. Comparing with Jaynes-Cummings model, the second-order correlation function at zero time delay g(2)(0) in our scheme can be reduced by two orders of magnitude and the system sustains a large intracavity photon number. A red (blue) cavity-light detuning asymmetry for photon quantum statistics with bunching or antibunching characteristics is also observed. The photon blockade effect has a controllable flexibility by tuning the relative phase between the two pumping laser fields and the Rabi coupling strength between the quantum dot and the pumping field. Moreover, the photon blockade scheme based on quantum interference mechanism does not require a strong coupling strength between the cavity and the quantum dot, even with the pure dephasing of the system. This simple proposal provides an effective way for potential applications in solid state quantum computation and quantum information processing.

A scheme for direct implementation of a two-target qubit controlled phase gate with quantum dots in coupled photonic crystal cavities without using classical laser pulses

We propose a scheme to implement a three-qubit controlled phase gate with one control qubit and two target qubits using quantum dots (QDs) in two coupled photonic crystal (PC) cavities A and B. In the scheme, three QDs are embedded in two coupled photonic crystal cavities and the transitions between the levels are only coupled to the cavity modes without being driven by the classical laser fields. We investigate the dynamics of the system consisting of resonant and off-resonant couplings between the cavity modes and QDs and solve the time-dependent Schrödinger equation analytically. The results show that a three-qubit controlled phase gate can be directly implemented using one operational step, by exchanging a single photon between the PC cavities A and B. This scheme greatly simplifies the gate operation in experiments.

Noise resistance of Toffoli gate in an array of coupled cavities

Two schemes of implementing the Toffoli gate are proposed in an array of coupled cavities. In the first one, two classical laser fields with fixed Rabi frequency are used via quantum Zeno dynamics. While in the second scheme, the invariant-based inverse engineering is used to implement the Toffoli gate, which can drive the instantaneous eigenstates to evolve exactly under the Schrödinger equation. The strictly numerical simulations are given and the influences of cavity decay and spontaneous emission on the Toffoli gate operation are analyzed with master equation. The result shows that our schemes for the Toffoli gate are robust against the decoherence because of the short time needed.

Interaction of a classical laser field with a model Rydberg atom in a mixed state prepared by entanglement with few-photon quantum light

The dynamics a model Rydberg atom prepared initially in a mixed state is investigated in a classical laser field. The possibility of interference stabilization regime is studied and the influence of parameters of initial mixed state on the ionization process is analyzed. In the case when initial atomic mixed state is formed due to entanglement with few-photon non-classical light the possibility to extract the information about initial atomic density matrix from the atomic behavior in the further applied classical laser field is discussed.

The influence of phase damping on a two-level atom in the presence of the classical laser field

In this paper we consider the influence of phase damping on the Jaynes–Cummings model (JCM) in the presence of the classical laser field. It is shown that for the temporal evolution of the atomic inversion a detuning parameter plays a role in delaying the effect of the damping. Our consideration is also extended to discuss the atomic Wehrl entropy and entropy squeezing. For the case of the marginal distribution, it is noted that the damping factor plays a considerable role in reducing the number of the fluctuations in the function behavior. On the other hand the damping factor removes the phenomenon of squeezing from both quadratures of the entropy squeezing.

Achieving slow and fast light with high transmission by nanodiamond nitrogen-vacancy center coupling to photonic crystal cavity

Using a single diamond nitrogen-vacancy (NV) center embedded in a waveguide-coupled photonic crystal (PC) nanocavity and driven by a classical laser field, we investigate optical transmission and group delay characteristics of the hybrid system operating in the weak-coupling regime. It is found that double electromagnetically induced-transparency (EIT) transmission peaks and slow- and fast-light propagation inside the EIT-like windows can be realized with practical system parameters. The double-frequency transparency of the input light expands the frequency range of EIT and may improve the controllability of EIT in this composite PC-NV system. The present system also provides a way to achieve integrated photonic slow- and fast-light devices for applications requiring multiple EIT effect in a PC platform.

Generation of four-atom Greenberger—Horn—Zeilinger state via adiabatic passage

We propose a scheme to generate a Greenberger—Horn—Zeilinger (GHZ) state of four atoms trapped in a two-mode optical cavity via an adiabatic passage. The scheme is robust against moderate fluctuations of the experimental parameters. Numerical calculations show that the excited probabilities of both the cavity modes and the atoms are tiny and depend on the pulse peaks of the classical laser fields. For certain decoherence due to the atomic spontaneous emission and the cavity decay, there exits a range of pulse peaks to get a high fidelity.

Directional emission of single photons from small atomic samples

We provide a formalism to describe deterministic emission of single photons with tailored spatial and temporal profiles from a regular array of multi-level atoms. We assume that a single collective excitation is initially shared by all the atoms in a metastable atomic state, and that this state is coupled by a classical laser field to an optically excited state which rapidly decays to the ground atomic state. Our model accounts for the different field polarization components via re-absorption and emission of light by the Zeeman manifold of optically excited states.

Geometric entangling gates for coupled cavity system in decoherence-free subspaces

We propose a scheme to implement geometric entangling gates for two logical qubits in a coupled cavity system in decoherence-free subspaces. Each logical qubit is encoded with two atoms trapped in a single cavity and the geometric entangling gates are achieved by cavity coupling and controlling the external classical laser fields. Based on the coupled cavity system, the scheme allows the scalability for quantum computing and relaxes the requirement for individually addressing atoms.

Preparation of steady-state entanglement via a laser-excited resonant interaction

In this paper we propose a scheme in which two-mode entanglement in a steady state is produced by using two lasers to resonantly drive a single four-level atom embedded inside a two-mode optical cavity. In this scheme, atomic coherence induced by a classical laser plays an important role in the process of preparing the entangled state. With the coupling of a strong control field, direct two-photon transition is generated and the relatively weak pump field induces the parametric interaction between two photons, which makes them entangle with each other. By numerical calculation, we find that the degree of entanglement depends strongly on the Rabi frequencies of the classical laser fields and the cavity losses.

Classical study of ultrastrong nonperturbative-field interactions with a one-electron atom: Validity of the dipole approximation for the bound-state interaction

We present a classical, relativistic Monte Carlo calculation investigating the role of the magnetic field in bound-state dynamics and ionization for atoms in ultrastrong external radiation fields. Atoms with atomic numbers $1\ensuremath{\leqslant}Z\ensuremath{\leqslant}20$ in external fields from 0.01 to ${10}^{3}$ a.u. are studied. We show that, when calculating ionization rates, the dipole approximation yields accurate values compared to a full classical electromagnetic laser field for intensities up to ${10}^{23}$ W/cm${}^{2}$. The calculations indicate that the quasistatic approximation is valid for external-field frequencies less than 1/20 of the Kepler-orbit time for the ionizing state. For ionization at fields above 100 a.u., the magnetic field affects the atom by altering the portion of the bound state that ionizes and deflecting the mean emission angle of the photoelectron angular distributions, although no change in the width of the final-state angular emission about this mean occurs. The photoelectron distribution and change in the ionizing bound state are seen as an indication of nonperturbative magnetic field effects for atoms in ultrastrong radiation fields.

Preparation of cluster states with trapped electrons on a liquid helium surface

We present a scheme for the preparation of one-dimensional (1D) and two-dimensional (2D) cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam. The two lowest levels of the vertical motion of the electron act as a two-level system, and the quantized vibration of the electron along one of the parallel directions (the x direction) serves as the bosonic mode. The degrees of freedom of the vertical and parallel motions of the trapped electron can be coupled together by a classical laser field. With the proper frequency of the laser field, the cluster states can be realized.

Generation of two-mode entangled states in a four-level atomic system via the Raman process

In this paper, we have theoretically investigated the generation of two-mode entangled states from a four-level atomic system via the Raman process. We show that the degree of entanglement between the two cavity modes could be strongly adjusted by both the Rabi frequencies and the detunings of the pumping fields. Our numerical results reveal that entanglement between the steady state of the two cavity modes depends on the difference of the two detunings of the atomic levels with the classical laser fields or the difference of the two Rabi frequencies. Finally, our result also shows that when such atomic system is operated above the threshold, it is possible to obtain the macroscopic entangled states.

Protocol for hybrid entanglement between a trapped atom and a quantum dot

We propose a quantum optical interface between an atomic and solid-state system. We show that quantum states in a single trapped atom can be entangled with the states of a semiconductor quantum dot through their common interaction with a classical laser field. The interference and detection of the resulting scattered photons can then herald the entanglement of the disparate atomic and solid-state quantum bits. We develop a protocol that can succeed despite a significant mismatch in the radiative characteristics of the two matter-based qubits. We study in detail a particular case of this interface applied to a single trapped ${^{171}\text{Y}\text{b}}^{+}$ ion and a cavity-coupled InAs semiconductor quantum dot. Entanglement fidelity and success rates are found to be robust to a broad range of experimental nonideal effects such as dispersion mismatch, atom recoil, and multiphoton scattering. We conclude that it should be possible to produce highly entangled states of these complementary qubit systems under realistic experimental conditions.

Optimal universal and phase-covariant quantum cloning machines with quantum-dot spins in cavity QED

Schemes for implementing a 1 → 2 optimal universal quantum cloning machine (UQCM) and a 1 → 3 ancilla-free optimal phase-covariant quantum cloning machine (PCCM) are proposed by manipulating the transverse spin–spin interactions of quantum dots mediated by a vacuum single-mode cavity. The interactions among different quantum dots are selectively controlled by the classical laser fields. These quantum cloning machines are more robust due to the very long spin decoherence time of quantum dots. Furthermore, the experimental implementation is simplified in comparison with those using atoms as qubits. The quantum dots are embedded in the cavity simultaneously; hence the troubles caused by the qubits passing through multiple cavities are effectively avoided.

Generation of fully three-mode continuous-variable entanglement in a single-atom laser

We proposed a scheme for generating fully three-mode continuous-variable (CV) entanglement between three nondegenerate cavity modes in a single-atom laser. In our scheme, the single-atom laser consists of a four-level atom inside a triply resonant cavity, and the atomic coherence is induced by two classical laser fields driving the corresponding atomic transitions. To demonstrate the generation of entanglement, we numerically simulated the dynamics of this system, and the numerical simulation shows that the single-atom laser considered here can be seen as a three-mode CV entanglement amplifier even in the presence of cavity losses. Moreover, we also show that the generation of entanglement doesn’t depend intensively on the initial condition of cavity field, and the fully three-mode CV entanglement can be realized no matter the three entangled (nondegenerate) modes are initially in the same state or different states based on our scheme.

Jaynes-Cummings models with trapped electrons on liquid helium

Jaynes-Cummings model is a typical model in quantum optics and has been realized with various physical systems (e.g, cavity QED, trapped ions, and circuit QED etc..) of two-level atoms interacting with quantized bosonic fields. Here, we propose a new implementation of this model by using a single classical laser beam to drive an electron floating on liquid Helium. Two lowest levels of the {\it vertical} motion of the electron acts as a two-level "atom", and the quantized vibration of the electron along one of the {\it parallel} directions, e.g., $x$-direction, serves the bosonic mode. These two degrees of freedom of the trapped electron can be coupled together by using a classical laser field. If the frequencies of the applied laser fields are properly set, the desirable Jaynes-Cummings models could be effectively realized.

Implementing 1 → M economical phase-covariant cloning and telecloning in cavity QED

We propose a scheme to implement 1 → M economical phase-covariant quantum cloning by using N three-level atoms nonresonantly interacting with a cavity assisted by a classical laser field. Using this interaction 1 → M telecloning is also implemented by applying the maximal entangled W state and partial entangled W state as the quantum channel, respectively. It is pointed out by analysing the fidelities and success probabilities that a relatively high fidelity and success probability can be obtained by choosing an appropriate channel in terms of the pre-known information of the input state.

Cavity-QED-based phase gate for photonic qubits

We present a two-qubit phase gate for photonic qubits using a three-level atom trapped in an optical cavity. In the scheme, the two ground states are coupled to the excited state by two cavity fields, respectively, and one of them is driven by a classical laser field. It is shown that, based on the large-detuning condition, the decay of atomic spontaneous emission can be effectively suppressed. The influence of cavity decay on our scheme is also investigated.

Nonequilibrium properties of strongly correlated artificial atoms—a Green's functions approach

A nonequilibrium Green's functions (NEGF) approach for spatially inhomogeneous, strongly correlated artificial atoms is presented and applied to compute the time-dependent properties starting from a (correlated) initial few-electron state at finite temperatures. In the regime of moderate-to-strong coupling, we consider the Kohn mode of a three-electron system in a parabolic confinement excited by a short-pulsed classical laser field treated in the dipole approximation. In particular, we numerically confirm that this mode is preserved within a conserving (e.g., Hartree–Fock or second Born) theory.