Two-level Trapped Ion Research Articles

Simultaneous suppression of decoherence of qubit induced by phase damping and heating effect in trapped ion system

In a single two-level trapped ion system, dynamical control of decoherence induced by phase damping involving electric motion of ion and heating effect involving vibrational motion of ion has been investigated. We have found that two kinds of decoherences can be simultaneously suppressed by applying a series of blue sideband and red sideband pulses to drive alternately the ion in a precision-designed manner, thus best results can be obtained with minimal resources.

Generation of Three-Qutrit Singlet States with Two-Level Trapped Ions**Supported by National Natural Science Foundation of China under Grant Nos. 61308012 and 61275215, by the Fujian Natural Science Foundation under Grant Nos. 2013J01008 and 2012J01004 and by the Fund from Fujian Educational Department under Grant Nos. JA14075, JB13021, and JB12014

We propose an adiabatic-passage scheme for the generation of three-qutrit singlet states with two-level trapped ions. Distinctly different from previous proposals, we encode qutrits in Dicke states with two-level ions and use the adiabatic-evolution techniques in order not to exactly control the laser pulses, making the realization of the scheme much easier. Furthermore, the phonon is only virtually excited in the procedure, so the effect of the phonon losses can be reduced.

Perturbative approach to the dynamics of a trapped ion interacting with a light field

We present a second-order perturbative analysis of the model describing a two-level trapped ion interacting with a travelling laser field, in the Lamb–Dicke regime. Unlike the customary approach, based on the interaction picture and the rotating wave approximation, we reduce the original Hamiltonian to a time-independent model, unitarily equivalent to a spin-boson model, which features a form well suited to apply the perturbation theory. We determine the first- and second-order corrections of eigenstates and eigenvalues. By varying the interaction parameters we identify four regimes characterized by different eigenvalue distributions (possibly including level doublets) and suggest the presence of an intermediate regime where the spectrum undergoes macroscopic changes. In this regime, where the perturbation approach does not hold, our reduced Hamiltonian is shown to reproduce the Jaynes–Cummings model.

Engineering of nonclassical motional states in optomechanical systems

We propose to synthesize arbitrary nonclassical motional states in optomechanical systems by using sideband excitations and photon blockade. We first demonstrate that the Hamiltonian of the optomechanical systems can be reduced, in the strong single-photon optomechanical coupling regime when the photon blockade occurs, to one describing the interaction between a driven two-level trapped ion and the vibrating modes, and then show a method to generate target states by using a series of classical pulses with desired frequencies, phases, and durations. We further analyze the effect of the photon leakage, due to small anharmonicity, on the fidelity of the expected motional state, and study environment induced decoherence. Moreover, we also discuss the experimental feasibility and provide operational parameters using the possible experimental data.

Transfer of Two Qubits States Using Coupled Cavities in Off-Resonance Systems

In this work we studied a system consisting of a pair of two-level trapped ions in coupled optics cavities, where we analyze the transfer of states of two qubits from the degrees of freedom (of movement and of internal states) of one ion to another. This system was studied near the blue side band frequency with a small gap. With analytical results obtained was possible to calculate the fidelity of transfer of entangled qubits.

Simultaneous Suppression of Spontaneous Emission and Thermal Effect in Two-Level Trapped Ion System

We have proposed a method to suppress simultaneously decoherence induced by spontaneous emission and thermal effect in a single two-level trapped ion system based on bang-bang scheme. The basic idea of this method is that two kinds of decoherences are both suppressed by using a series of large detuned pulses to drive the ion in a precision-designed manner, thus best results can be obtained with minimal resources.

Singularities in ion trap nonlinear coherent states

We present a theoretical analysis of the k-boson nonlinear coherent states of a two-level trapped ion interacting with two laser fields. Such states are both the zero-energy state of the interaction Hamiltonian and the eigenstates of a deformed annihilation operator. For the single-boson case, we show that the structure of the states and their coherence and minimum-uncertainty properties can be compromised whenever the Lamb–Dicke parameter is one of the roots of certain Laguerre polynomials. We investigate these problems, which are strictly related to the non-analyticity of the deformation function in the annihilation operator.

A NEW PARAMETER OF ENTANGLEMENT FOR A QUBIT SYSTEM PLACED INSIDE A DISSIPATIVE CAVITY

The entanglement in a system of a single two-level trapped ion and a single-mode quantized field in a coherent state inside a phase-damped cavity is investigated. Analytic results under certain parametric conditions are obtained, by means of which we analyze the influence of dissipation on the atomic Fisher information and its marginal distribution. An interesting relation between the temporal entanglement sudden birth, sudden death, atomic Fisher information and the dissipation effect is observed.

Quantum logic gates with two-level trapped ions beyond Lamb–Dicke limit

In the system with two two-level ions confined in a linear trap, this paper presents a simple scheme to realize the quantum phase gate (QPG) and the swap gate beyond the Lamb–Dicke (LD) limit. These two-qubit quantum logic gates only involve the internal states of two trapped ions. The scheme does not use the vibrational mode as the data bus and only requires a single resonant interaction of the ions with the lasers. Neither the LD approximation nor the auxiliary atomic level is needed in the proposed scheme. Thus the scheme is simple and the interaction time is very short, which is important in view of decoherence. The experimental feasibility for achieving this scheme is also discussed.

Dynamics of Two-Level Trapped Ion in a Standing WaveLaser in Noncommutative Space

We study the dynamics of a two-level trapped ion in a standingwave electromagnetic field in two-dimensional (2D) noncommutativespaces in the Lamb–Dicke regime under the rotating waveapproximation. We obtain the explicit analytical expressions forthe energy spectra, energy eigenstates, unitary time evolutionoperator, atomic inversion, and phonon number operators. The Rabioscillations, the collapse, and revivals in the average atomicinversion and the average phonon number are explicitly shown tocontain the information of the parameter of the spacenoncommutativity, which sheds light on proposing new schemes basedon the dynamics of trapped ion to test the noncommutativity.

Quantum logic gates with a two-level trapped ion in a high-finesse cavity beyond the Lamb–Dicke limit

In the system with a two-level ion confined both in a linear trap and in a high-Q single-mode cavity, we present a simple scheme to realize the basic two-qubit logic gates such as the quantum phase gate (QPG), the SWAP gate and the controlled-NOT (CNOT) gate beyond the Lamb–Dicke (LD) limit. We realize the three kinds of two-qubit quantum phase gates, i.e. QPG operation involving the cavity mode as well as the vibrational mode of the trapped ion, QPG operation involving the internal states as well as the vibrational mode of the trapped ion and QPG operation involving the internal states of the trapped ion as well as the cavity mode. The controlled-NOT gate can be implemented from a QPG operation through a rotation of the second qubit before and after the QPG operation. We can also perform the SWAP gate operation involving the ionic internal states of the trapped ion and the two-mode bosonic basis. The logic gates involving the cavity mode as well as the vibrational mode of the trapped ion are insensitive to spontaneous emission, and the logic gates involving the internal states as well as the vibrational mode of the trapped ion are insensitive to the decay of the cavity, which is an important feature for the practical implementation of quantum computing. Neither the LD approximation nor the auxiliary atomic level is needed in our scheme. Experimental feasibility for achieving our scheme is also discussed.

Dynamics of a two-level trapped ion in a cavity

In the present paper we consider the case of a two-level ion in a cavity in the presence of a single mode field linearly polarized. We suppose that the ion is free to move along the polarization direction and trapped by a harmonic potential along the other two directions. By multiple path integration we derive the density matrix of the system and we study its dynamics. We assume an initial electromagnetic vacuum. This initial condition for the present system, compared with any other initial photonic state, gives new and higher order leading terms with respect to an expansion in powers of the inverse of the volume. Further after such an expansion there appears a first order term that originates from the combined interaction of the two-level system (qubit) with the quantum motion of the ion and the electromagnetic field in the cavity. We notice that the dynamics of the present system is very rich and can be studied exhaustively in the present framework.

Effective cross-Kerr nonlinearity and robust phase gates with trapped ions

We derive an effective Hamiltonian that describes a cross-Kerr type interaction in a system involving a two-level trapped ion coupled to the quantized field inside a cavity. We assume a large detuning between the ion and field (dispersive limit) and this results in an interaction Hamiltonian involving the product of the (bosonic) ionic vibrational motion and field number operators. We also demonstrate the feasibility of operation of a phase gate based on our hamiltonian. The gate is insensitive to spontaneous emission, an important feature for the practical implementation of quantum computing.

Coherent-state superpositions in cavity quantum electrodynamics with trapped ions

We investigate how superpositions of motional coherent states naturally arise in the dynamics of a two-level trapped ion coupled to the quantized field inside a cavity. We extend our considerations including a more realistic set up where the cavity is not ideal and photons may leak through its mirrors. We found that a detection of a photon outside the cavity would leave the ion in a pure state. The statistics of the ionic state still keeps some interference effects that might be observed in the weak coupling regime.

Quantum computation with two-level trapped cold ions beyond Lamb-Dicke limit

We propose a simple scheme for implementing quantum logic gates with a string of two-level trapped cold ions outside the Lamb-Dicke limit. Two internal states of each ion are used as one computational qubit (CQ) and the collective vibration of ions acts as the information bus, i.e., bus qubit (BQ). Using the quantum dynamics for the laser-ion interaction as described by a generalized Jaynes-Cummings model, we show that quantum entanglement between any one CQ and the BQ can be coherently manipulated by applying classical laser beams. As a result, universal quantum gates, i.e. the one-qubit rotation and two-qubit controlled gates, can be implemented exactly. The required experimental parameters for the implementation, including the Lamb-Dicke (LD) parameter and the durations of the applied laser pulses, are derived. Neither the LD approximation for the laser-ion interaction nor the auxiliary atomic level is needed in the present scheme.

Universal quantum computation with two-level trapped ions

Although the initial proposal for ion trap quantum computation made use of an auxiliary internal level to perform logic between ions, this resource is not necessary in principle. Instead, one may perform such operations directly using sideband laser pulses, operating with an arbitrary (sufficiently small) Lamb-Dicke parameter. We explore the potential of this technique, showing how to perform logical operations between the internal state of an ion and the collective motional state and giving explicit constructions for a controlled-not gate between ions.

Efficient Scheme for the Deterministic Maximal Entanglement ofNTrapped Ions

We propose a method for generating maximally entangled states of $N$ two-level trapped ions. The method is deterministic and independent of the number of ions in the trap. It involves a controlled NOT acting simultaneously on all the ions through a dispersive interaction. We explore the potential application of our scheme for high precision frequency standards.