L. A. Gushchin

Cavity-assisted atomic frequency comb memory in an isotopically pure 143Nd3+ :YLiF4 crystal

In this work we present an implementation of cavity-assisted atomic frequency comb (AFC) memory protocol in an isotopically pure 143Nd3+ :YLiF4 crystal. We use a tunable confocal Fabry–Perot cavity that is placed inside the cryostat. For a 1 mm thick sample with optical depth of 0.2 we obtain total storage efficiency of 3%, which is a 15-fold enhancement compared to the no cavity case. The memory bandwidth is limited by the inhomogeneous broadening of the optical transition and allows us to store short 30 ns pulses.

Atomic frequency comb memory in an isotopically pure 143Nd3+:Y7LiF4 crystal

We implemented the atomic frequency comb protocol for optical quantum memory in an isotopically pure crystal of Y7LiF4 doped by 143Nd3+ ions. Echo signals were observed on the 4I9/2(1)–4F3/2(1) transition, which had inhomogeneous broadening much smaller than the hyperfine splitting of the ground and excited states. We performed hole-burning spectroscopy measurements on several transitions, obtaining information about the hyperfine state lifetimes. An intrinsic hole structure was found on some of the transitions, which allowed us to prepare a comb structure with two clearly defined periods and to observe echo pulses with different time delays.

Single-qubit gates for ensemble qubits via off-resonant Raman interaction

In this paper we analyze the fidelity of single-qubit gates based on off-resonant Raman interaction when they are applied to qubits implemented as ensembles of active centers. In particular, we investigate the additional errors induced by the inhomogeneous broadening of the qubit ensemble. We propose a new scheme which can be used to significantly decrease these errors and to realize high-fidelity logic gates for ensemble qubits.

Qubits based on spectrally selected groups of Pr3+ ions in a LaF3 crystal

Spectral selection, i.e., the separation of a group of particles with a spread in resonance frequencies smaller than the hyperfine splitting of working levels has been implemented by the method of burning of long-lived spectral dips in the inhomogeneously broadened absorption line of Pr3+ in a LaF3 crystal. The possibility of implementing qubits (basic elements of quantum computations) on ensembles of spectrally selected particles and the main operations with them, including the manipulation of the populations of hyperfine (qubit) levels and the controlled shift of the absorption line of one spectrally selected group of ions upon excitation of another group (two-qubit operations), has been demonstrated. The decay rates of the population of hyperfine sublevels of the ground state of the spectrally selected group of particles have been measured.

Demonstrating the Possibility of Implementing the Toffoli Gate in Crystals Doped by Rare-Earth Metal Ions

A scheme for the implementation of the Toffoli gate in inorganic crystals doped by rare-earth metal ions is proposed. A numerical analysis of the factors affecting the fidelity of the Toffoli gate implementation is carried out, and estimates for the available experimental parameters are obtained. A demonstration experiment is set up in which behavior similar to the Toffoli gate is shown for ensembles of Pr3+ ions doped into a LaF3 crystal.

Photon echo in an atomic frequency comb in a Pr-doped LaF3 crystal

The possibility of storage of an optical pulse in a memory based on an atomic frequency comb in a Pr3+:LaF3 crystal is demonstrated experimentally. A new method of storage-time control using an external electric field is proposed and experimentally implemented.

Effective regime of electromagnetically induced transparency in a Pr3+:LaF3 crystal

The results of experimental and numerical investigations of electromagnetically induced transparency in a Pr3+:LaF3 crystal have been presented. A spectrally isolated Λ system has been made of a specially prepared medium of an ensemble of particles with an inhomogeneous width less than the hyperfine splitting of both upper and lower operating levels. A considerable increase in the transmittance with respect to an unprepared medium has been demonstrated. It has been shown that, under the experimental conditions, the transmittance is limited by the apparatus (spread of the transmission peak by the instrumental linewidth specified by the probe pulse length).

Using coherent population trapping in test atoms for magnetic field measurements in toroidal plasmas

A way to measure the profile of the safety factor in toroidal controlled-fusion setups has been developed. The method is based on measuring the ratio of the poloidal magnetic field and the toroidal one locally, based on a modification of the optical resonance-fluorescence signal. The effect of partial suppression of resonance fluorescence is used, which depends on the orientation of the magnetic field relative to the laser beam, and takes place in case of coherent population trapping in test atoms with the Zeeman split-level structure, as affected by double-frequency laser radiation.

Electromagnetically induced transparency on Zeeman sublevels in Nd3+:LaF3 crystals

The results of experimental observation of the electromagnetically induced transparency regime on the 4I9/2-4G5/2 transition in Nd3+ ions doping in LaF3 are presented. The depth and width of the transparency are analyzed as functions of the control field intensity.

On the possibility of reducing the influence of laser radiation linewidth on execution of quantum logic operations using off-resonant Raman interaction

We investigate the possibility of reducing negative influence of the laser radiation linewidth on execution of quantum logical operations using off-resonant Raman interaction.