Heterogeneous atomic qubits for realizing second-order equilibrium coherence time in Precision Measurement Institute

[ Instrument R & D of Instrument Network ] Recently, the team of researcher Zhan Mingsheng of the Institute of Precision Measurement Science and Technology Innovation of the Chinese Academy of Sciences has made new progress in the coherent manipulation of heterogeneous atomic qubits. The team first applied the magic light intensity dipole trap (MI-ODT) technology they first implemented [Phys.Rev.Lett.117,123201 (2016)] to a heterogeneous atom qubit array in which two atoms coexist, and for each One atom achieves coherence time on the order of seconds. They further introduced laser polarization as a new control parameter in MI-ODT, so that in the same set of control parameters, both atoms have a longer coherence time, and the coherence time balance of the two types of qubit superposition states is achieved. And both are raised to about 1 second.

The neutral atom system in the optical trap array exhibits excellent scalability, so it has broad application prospects in quantum simulation and quantum computing. However, after the expansion of the number of qubits, it is inevitable that the crosstalk problem in the operation of quantum logic and the initialization and state reading of qubits will become prominent. A possible way to effectively avoid crosstalk is to use heterogeneous atom resonance frequencies to establish heterogeneous atom qubit systems. Such a system can be used to perform different tasks in quantum computing.For example, one of the atomic qubits is used as the checksum in the error correction code, and the other atom is used as the data qubit, so it is possible to effectively perform error correction and To avoid crosstalk; it can also be used in quantum simulation, because the additional control freedom provides conditions for the simulation of multi-component multi-spin systems. Therefore, heterogeneous atomic systems have potentially broad application prospects in the fields of quantum simulation, quantum computing, and quantum precision measurement.

There is no clear definition of qubits. Different researchers use different expressions. For example, from the perspective of physics, people are accustomed to called qubits (qubits or qbits) or entangled bits (ebits) according to the characteristics of quantum states , Tribit, tribit, multibit and cbit, etc. This way is dazzling, and the description of qubits should be based on specific physical characteristics. In order to avoid these problems, here is a unified description of qubits from the perspective of information theory.

On the road to quantum information of heterogeneous atoms, the team has demonstrated for the first time in 2017 the quantum controlled NOT gate between two atoms of different nuclei and the quantum entanglement of two atoms of different nuclei [Phys.Rev.Lett. 119 , 160502 (2017)]. Another key element to expand from the same kind of system to the different kind of system is to achieve the storage of heterogeneous atomic qubits with long coherence time and balance. The life of the state is not conducive to the implementation of quantum information processing.

Recently, associate researcher He Xiaodong and doctoral student Guo Ruijun and others further developed the MI-ODT method and successfully implemented two 3 × 3 cross-arrangement polarization coordinated magic light intensity dipole trap arrays of heterogeneous systems. The heterogenous system of atomic magic light trapping technology relies on the third-order cross-term coefficients of atoms and the tunability of the ground state hyperpolarizability. The ground state hyperpolarizability essentially depends on the circular polarization of the trapped light field.

If the light vector at each point in the direction of light propagation is in a certain plane, this light is called plane polarized light. If the locus of the end point of the light vector is a straight line, the plane polarized light at this time is also called linear polarization For light, the trajectory of the end of the electric vector of light on a plane perpendicular to the direction of propagation is a linearly polarized light [1]. When the two propagation directions are the same, the vibration directions are perpendicular to each other, and the phase difference is constant φ = (2m ± 1/2) π, the two plane polarized lights can be superimposed to synthesize circularly polarized light with regular change of light vector. The magnitude of the electric vector of circularly polarized light remains unchanged, while the direction changes with time. When the phase difference is φ = (2m + 1/2) π, it is left-handed circularly polarized light, and when the phase difference is φ = (2m-1 / 2) π, it is right-handed circularly polarized light.

Experimentally, the polarization degree of the dipole trap array loaded with 85Rb atoms is precisely adjusted to a certain value, so that the compensation magnetic field required by the magic light trapping technology is equal to the magic in another fully circularly polarized dipole trap array. Light intensity traps the compensation magnetic field required for 87Rb atomic qubits. In this polarization-aligned magic light intensity dipole trap array, the coherence time of the superposition state of 85Rb and 87Rb atomic qubits is increased to 891 ± 47 ms and 943 ± 35 ms, respectively. Compared with the gate operation time on the order of microseconds of single-qubit and double-qubit logic gates of atoms, the obtained coherence time of atomic internal states on the order of seconds meets the requirements of coherence of qubits in the general quantum computer criterion .

The research result is the further expansion and application of the MI-ODT technology developed by the team in heteronuclear systems, highlighting the value of the original technology in the research of neutral atom quantum computing, for the construction of heteronuclear atoms that can extend the long coherence time The quantum information processor has taken another crucial step forward.

Source: Encyclopedia, Institute of Precision Measurement Science and Technology Innovation