Resonant Optical Pulses Research Articles

Variational quantum state preparation via quantum data buses

We propose a variational quantum algorithm to prepare ground states of 1D lattice quantum Hamiltonians specifically tailored for programmable quantum devices where interactions among qubits are mediated by Quantum Data Buses (QDB). For trapped ions with the axial Center-Of-Mass (COM) vibrational mode as single QDB, our scheme uses resonant sideband optical pulses as resource operations, which are potentially faster than off-resonant couplings and thus less prone to decoherence. The disentangling of the QDB from the qubits by the end of the state preparation comes as a byproduct of the variational optimization. We numerically simulate the ground state preparation for the Su-Schrieffer-Heeger model in ions and show that our strategy is scalable while being tolerant to finite temperatures of the COM mode.

Resonant optical pulses on a continuous-wave background in two-level active media

We present exact N-soliton optical pulses riding on a continuous-wave (c.w.) beam that propagate through and interact with a two-level active optical medium. Their representation is derived via an appropriate generalization of the inverse scattering transform for the corresponding Maxwell-Bloch equations. We describe the single-soliton solutions in detail and classify them into several distinct families. In addition to the analogues of traveling-wave soliton pulses that arise in the absence of a c.w. beam, we obtain breather-like structures, periodic pulse-trains and rogue-wave–type (i.e., rational) pulses, whose existence is directly due to the presence of the c.w. beam. These soliton solutions are the analogues for Maxwell-Bloch systems of the four classical solution types of the focusing nonlinear Schrödinger equation with non-zero background, although the physical behavior of the corresponding solutions is quite different.

Manipulation of resonant Auger processes using a strong bichromatic field

We theoretically investigate the effects of strong couplings in resonant Auger processes under the combination of strong resonant x-ray and nearly resonant optical pulses. The x-ray field couples the ground state with a core-excited state, while the optical field couples the core-excited state with another core-excited state of opposite parity. The Auger electron spectrum changes its shape as the intensities of the x-ray and/or optical fields increase, and at sufficiently high intensities we observe that the splitting, which is induced by the optical field, is superposed on the asymmetric splitting induced by the x-ray field in the Auger electron spectra. The asymmetric splitting itself, which is induced by the strong x-ray pulse, is persistent but modified due to the presence of the strong optical field. Moreover, through the systematic study by including or excluding the individual photoionization processes from the core-excited states and the direct photoionizaton process from the ground state, we clarify the contribution of the respective processes to the total electron yield and the Auger electron spectra. These results show that we can manipulate the resonant Auger processes through the introduction of the second core-excited state and the strong optical field.

Tunneling of Conduction Band Electrons Driven by a Laser Field in a Double Quantum dot: An Open Systems Approach

In this paper, we investigate tunneling of conduction band electrons in a system of an asymmetric double quantum dot which interacts with an environment. First we consider the case in which the system only interacts with the environment and demonstrate that as time goes to infinity they both reach an equilibrium, which is expected, and there is always a maximum and minimum for the populations of the states of the system. Then we investigate the case in which an external resonant optical pulse (a laser) is applied to the system interacting with the environment. However, in this case for different intensities we have different populations of the states in equilibrium and as the intensity of the laser gets stronger, the populations of the states in equilibrium approach the same constant.

Dissipative preparation of the exciton and biexciton in self-assembled quantum dots on picosecond time scales

Pulsed resonant fluorescence is used to probe ultrafast phonon-assisted exciton and biexciton preparation in individual self-assembled InGaAs quantum dots. By driving the system using large area $(\ensuremath{\ge}10\ensuremath{\pi})$ near resonant optical pulses, we experimentally demonstrate how phonon-mediated dissipation within the manifold of dressed excitonic states can be used to prepare the neutral exciton with a fidelity $\ensuremath{\ge}70%$. By comparing the phonon-assisted preparation with resonant Rabi oscillations we show that the phonon-mediated process provides the higher-fidelity preparation for large pulse areas and is less sensitive to pulse area variations. Moreover, by detuning the laser with respect to the exciton transition, we map out the spectral density for exciton coupling to the bulk LA-phonon continuum. Similar phonon-mediated processes are shown to facilitate direct biexciton preparation via two-photon biexciton absorption, with fidelities $>80%$. Our results are found to be in very good quantitative agreement with simulations that model the quantum dot--phonon bath interactions with Bloch-Redfield theory.

Coherence of an electron spin in quantum dots generated by a resonant optical pulse with elliptic polarization

We have experimentally observed the spin polarization process of single electrons in InP/InGaP quantum dots by time-resolved Kerr rotation measurements. It is found that the inversion of the spin polarization direction occurs with the variation of the intensity of the optical pulse. The spin coherence lifetime abruptly changes on the occurrence of the inversion. We have reproduced the inversion in numerical simulations using the density operator of the electron–trion four-level system, assuming a small deviation of the optical pulse from circular polarization. The change of the spin lifetime is attributed to the qualitative change of the four-level system in the electric polarization state.

Picosecond optical spectroscopy of a single negatively charged self-assembled InAs quantum dot

We demonstrate an experimental technique for the transient read-out of the optical transitions in a single negatively charged self-assembled InAs quantum dot (QD) using resonant picosecond optical pulses and control of the QD charge state. Observable phenomena include trion (negatively charged exciton) decay, Rabi oscillations between the electron and trion states and the precession of electron and heavy-hole spins about an externally applied dc magnetic field.

Charge qubit entanglement via conditional single-electron transfer in an array of quantumdots

We propose a novel scheme to generate entanglement among quantum-dot-based chargequbits via sequential electron transfer in an auxiliary quantum dot structure whosetransport properties are conditioned by qubit states. The transfer protocol requires theutilization of resonant optical pulses combined with an appropriate voltage gatepattern. As an example illustrating the application of this scheme, we examine thenine-qubit Shor code state preparation together with the error syndrome measurement.

Analysis of Dynamic Switching Behavior of Bistable Semiconductor Ring Lasers Triggered by Resonant Optical Pulse Injection

The relaxation oscillation and decay toward steady state following the switching of the lasing direction in a bistable semiconductor ring laser triggered by resonant optical pulse injection is studied theoretically using small-signal method. Analytical expressions for damping factor, relaxation oscillation frequency, and the decay time are derived. Calculation results based on the expressions derived are compared with numerical simulations, and good agreement is observed. It is shown that the dynamic behavior can be greatly improved by increasing the differential gain, photon density, optical confinement factor, and nonlinear gain compression coefficient, as well as by decreasing the photon lifetime.

Generation of coherent terahertz pulses in ruby at room temperature

We have shown that a coherently driven solid state medium can potentially produce strong controllable short pulses of THz radiation. The high efficiency of the technique is based on excitation of maximal THz coherence by applying resonant optical pulses to the medium. The excited coherence in the medium is connected to macroscopic polarization coupled to THz radiation. We have performed detailed simulations by solving the coupled density matrix and Maxwell equations. By using a simple $V$-type energy scheme for ruby, we have demonstrated that the energy of generated THz pulses ranges from hundreds of pico-Joules to nano-Joules at room temperature and micro-Joules at liquid helium temperature, with pulse durations from picoseconds to tens of nanoseconds. We have also suggested a coherent ruby source that lases on two optical wavelengths and simultaneously generates THz radiation. We discussed also possibilities of extension of the technique to different solid-state materials.

Quantum Gates Based on Electron Spins of Triple Quantum Dot

Quantum computation using electron spins in three-coupled dots of different sizes is proposed. By using photon-assisted tunnelling, Coulomb blockade and spin rotation of electrons, logic gates are realized by static and rotational magnetic fields and resonant optical pulses. The two-bit CNOT is numerically demonstrated by the time evolution of the density matrix. In addition, the Hamiltonian is described using pseudo-spin representation and the phase change during the gate operation is discussed.

Experimental coherent control of lasers

We experimentally demonstrate coherent control of a laser. A resonant 100-fs optical pulse is injected into a vertical cavity surface emitting laser to introduce a field component with well-defined phase and thereby excite beating oscillations between the transverse lasing modes. By changing the relative phase between two injected pulses, we can enhance or destroy the beating oscillations and select which lasing modes are excited. We discuss resonant pulse injection into lasers and show how mode competition improves controllability by suppressing the phase-sensitive effects of the carriers.

Rabi frequency and optical Bloch equations for a short femtosecond optical pulse

We investigate the interaction of a multilevel atom with a short femtosecond optical pulse beyond the scope of the rotating-wave approximation. We consider the behavior of a three-level atom under the action of two optical pulses resonant with two allowed transitions and a two-level atom under the action of a resonant optical pulse. It is shown that the imaginary part of the off-diagonal elements of the density matrix oscillates with high frequency due to the counter-rotating terms. It is shown also that an effective time-dependent addition to the Rabi frequency exists, which is of importance for ultrashort optical pulses.

Quantum gates using spin states of triple quantum dot

We present a new model of quantum gates using electron spins of triplely coupled quantum dots. By using the energy selectivity of both photon-assisted tunneling and spin rotation of electrons, logic gates are realized by static and rotational magnetic field and resonant optical pulses. We used what we call a “tunneling qubit”, which realized the switching of interaction between quantum bits. Possibility of the extension to many-qubit-system is also discussed.

Two-dimensional vibrational spectroscopy. VII. Investigation of the vibronic and vibrational couplings by using novel triply resonant two-dimensional vibrational spectroscopies

A single vibrational coherence state can be created by using either vibrationally resonant infrared field-matter interactions or Raman transitions induced by the electronically off-resonant fields. Then, the two-dimensional (2D) vibrational coherence created by two such interactions can be probed by using electronically off-resonant optical pulse via scattering by the 2D transient grating. However, due to the off-resonant field-matter interactions during the probing process, the signal intensity is likely to be small. Thus, in this paper, the cases when the 2D transient grating is probed by electronically resonant optical pulse are theoretically considered and the associated nonlinear response functions are investigated. It turns out that these novel 2D vibrational spectroscopic methods utilizing an electronically resonant probe pulse can be used to study both the linear and quadratic vibronic coupling strengths of molecules in either isotropic or anisotropic condensed phases, in addition to the vibrational anharmonicity and nonlinearity of the coordinate dependencies of the dipole moment, polarizability, and hyperpolarizability.

Propagation of high-intensity short resonant pulses in inhomogeneously broadened media

We investigate the areas of extremely short, intense (area ⩾π) resonant optical pulses on propagation through an inhomogeneously broadened atomic medium. Experimentally, there is no apparent change in the shape of such pulses on propagation, in contradiction to the area theorem. Here we show that, although the main part of the pulse is unchanged for short propagation distances (αl∼1), it is followed by a long weak tail formed by free induction decay from the excited atoms. The tail lengthens and oscillates on propagation through the medium and permits the area theorem to be obeyed. These oscillations, which depend critically on the Doppler broadening, are reflected in the spectral analysis of the propagated pulse. We also introduce another mechanism for pulse reshaping, which is a generalization of the McCall–Hahn pulse breakup and operates at long propagation lengths (αl≫1), where the number of absorbing atoms encountered by the pulse is comparable with the number of photons in the pulse.

Spin coherence excitation and rephasing with optically shelved atoms

We investigate the use of resonant optical Raman pulses to excite and rephase ground state spin coherences via the partial storage or shelving of atoms. Unlike direct-rf-excited spin echoes or off-resonant Raman echoes, the resonant Raman optical field efficiently excites and rephases the spin coherence using \ensuremath{\pi} and 2\ensuremath{\pi} pulses, respectively. In a crystal of ${\mathrm{Pr}}^{3+}$ doped ${\mathrm{Y}}_{2}{\mathrm{SiO}}_{5},$ we experimentally observe spin echo efficiency as high as 46% of the free induction decay signal.

Near dipole-dipole effects in electromagnetically induced transparency.

We present numerical calculations on the propagation of resonant optical pulse pairs in an absorbing medium of three-level \ensuremath{\Lambda} systems taking into account near dipole-dipole (NDD) interactions. We find that the NDD interactions reduce the effect of the electromagnetically induced transparency and the pulse group velocity. The NDD effect on phase modulation is also studied.

Multiple-pulse excitation of molecular vibration in resonant pump-probe experiments. Irradiation of π pulses

The induced transmittance measurement with intense resonant optical pulses is formulated. The non-perturbative solution of the Liouville equation predicts remarkable effects of the multiple excitation by π pulses. The feasibility of mode selective excitation in a multimode system is demonstrated by numerical calculations.

Three-state systems driven by resonant optical pulses of different shapes

New analytic solutions to the problem of a three-state system driven simultaneously by resonant optical pulses of different shapes are presented. The solutions are useful for prescribing the conditions for complete population transfer from one state to another or for complete population return.