Том 164, № 2 (2023)

The implementation of a quantum logic gate in a system of cold atoms in optical microtraps is analyzed. The dynamics of two spin qubits is simulated, and a number of processes that limit the efficiency of entanglement based on the Rydberg blockade effect are considered. A geometry of two-photon excitation of Rydberg states of atoms is proposed that makes it possible to increase the robustness of the system to variations in a number of parameters and to reduce losses associated with the incoherent scattering of the driving field.

Reply to the comment of P.L. Chapovsky to the paper “Symmetry approach in the problem of gas expansion into vacuum,” JETP 159, 794 (2021).

We propose a design of a source of cold thulium atoms based on a 2D magneto-optical trap and perform numerical simulation of its operation. Optimal parameters of cooling radiation and the magnetic field are determined; it is shown that for a total radiation power of 50 mW and an atomic oven temperature of 800 K, the proposed configuration can provide a flux of 4 × 10⁸ cold atoms per second, and with an increase of the oven temperature, the flux can reach ~ 10¹¹ atom/s. Such a source can be used for building frequency standards as well as in experiments with quantum simulators and the Bose–Einstein condensate.

Synchronous comparison of optical clocks using phase-coherent clock lasers makes it possible to determine the difference (ratio) of clock transition frequencies, which is not limited by the total noise of lasers in use. A detailed simulation of the comparison of two thulium optical clocks is performed using synchronous interrogation of atoms by the radiation of a common clock laser. Some critical parameters have been determined, specifically: the residual noncorrelated frequency and amplitude noises of test pulses and reading noises, which may deteriorate the comparison stability. At the same time, it is demonstrated that this way is insensitive to fluctuations in the number of atoms, calibration of feedback-loop parameters, individual ejections in measurement cycles, and fluctuations of laboratory magnetic field.

A quantum algorithm for solving the traveling salesman problem by the quantum phase estimation and quantum search method is considered. An approach is developed that was previously proposed for solving this problem. A quantum register is used to encode the eigenstates of a unitary operator whose phase determines the length of each possible route. The quantum phase estimation algorithm is used to estimate the length of a route. Then, to find the minimum route length, the measured values of length are encoded into the states of the second quantum register, and the search for the optimal route is carried out using a modified Grover algorithm. Numerical simulation of the proposed quantum algorithm is carried out using the Qiskit library for one and two iterations of the modified Grover algorithm.

We study the field shift of coherent population trapping (CPT) resonance excited by a bichromatic field in an open Λ system with account for the Gaussian profile of the laser radiation intensity. Two methods for error signal formation are considered: the harmonic frequency modulation and the step phase modulation (phase jumps). It is shown that the spatial inhomogeneity of the light beam leads to an essentially nonlinear dependence of the error signal shift on the laser radiation intensity. We propose an approach for the linearization of this dependence, which is important for the development of methods for suppressing the field shift in atomic clocks based on CPT resonances.

Standard methods of laser cooling ¹⁷¹Yb⁺ in a radiofrequency trap involve the use of coherent optical fields resonant to the optical transition of the ²S_1/2 → ²P_1/2 line, as well as a magnetic field that is used to destroy the coherent population trapping (CPT) appeared at the ²S_1/2(F = 1) level. Further precision measurements with use of the clock transitions (quadrupole ²S_1/2(F = 0) → ²D_3/2(F = 2) and octupole ²S_1/2(F = 0) → ²F_7/2(F = 2)) require significant suppression and control of residual magnetic fields. In this work, we investigate in detail an alternative method of laser cooling ¹⁷¹Yb⁺ with use of polychromatic fields, which allows completely eliminate the use of a magnetic field in the ion cooling process and thus suppress Zeeman quadratic shift associated with uncontrolled residual magnetic fields.

The absorption of a light wave interacting with optical transitions in the D₁ line of an alkali metal atom subjected to microwave radiation that is in resonance with magnetic dipole transitions between hyperfine ground-state components, has been investigated. It is known that when scanning a longitudinal magnetic field (B || k, where k is the wavevector), one may observe a magneto-optical resonance due to the ground-state Hanle effect. In addition, the effect of double radio-optical resonance takes place because of the presence of the resonance microwave field. The joint influence of these effects on the formation of a narrow magneto-optical resonance in light wave absorption has been studied theoretically and experimentally. It has been shown analytically that the effects compete with each other and destructively act on the resonance formation. As a result, the amplitude of the resonance is small and its shape is complicated. However, in the presence of a buffer gas the pressure of which is such that the hyperfine splitting of the ground state remains spectrally unresolved, it becomes possible to observe a magneto-optical resonance with a relatively large amplitude. Experiments have been carried out with the use of a miniature glass cell (V ~ 0.1 cm³) filled with ⁸⁷Rb vapor and a buffer gas argon (a pressure of about 95 Torr). In particular, the theoretically predicted resonance narrowing with increasing light field intensity has been experimentally observed. A configuration for magneto-optical resonance excitation suggested here may be applied in quantum magnetometry to measure weak permanent magnetic fields and resonance microwave fields using cells filled with alkali metal vapor.