Investigation Of Coherent Properties Of Mixed-species Atomic Qubits In An Optical Dipole Trap Array

Neutral atoms confined in an closely spaced array of optical dipole traps manifest outstanding scalability and thus are intensively developed for quantum simulation and quantum computation.Recently,atom-by-atom assemblers of defect-free atomic arrays have been demonstrated to deterministically pack 50 qubits into the 1D,2D and more qubits into the 3D spaces with relatively compact spacing between qubits.Based on these advances,a 51-atom quantum simulator has been demonstrated.The above achievements are important steps along the path of converting the scalability promise of neutral atoms into reality.However,when scaling neutral-atom systems to greater number and density of qubits,the problem of crosstalk shows up,which arises from imperfectly isolated logic operation and state readout and initialization of individual qubits.To mitigate crosstalk in the multi-qubits quantum processers,it has been recognized that extending the same-species qubits to the mixed-species ones,one for the data qubits and the other for the ancillary qubits,is one of the reliable approaches to circumventing the unwanted crosstalk during preparation,logic,and measurement operations.To date,coherence times of mixed-species qubits are greatly unbalanced so that the strong decoherence in the ancillary qubits is mainly responsible for the detected error in mixed-species logic gates and the measurement.Here,we construct a polarization-mediated magic-intensity optical dipole trap array,in which the detrimental effects of light shifts on the mixed-species qubits are efficiently mitigated so that the coherence times of the mixed-species qubits are substantially enhanced to nearly 1s.In order to realize such a long-lived and balanced mixed-isotope memory,we did the following three works:1.Increasing the coherence time of 87Rb qubit in the MI-ODT to 1 s.The homogenous dephasing from the magnetic field noise dominates the decay time of the Ramsey fringe 87Rb qubits.We choose to implement an active magnetic field stabilization.The resulting short-term stability is improved from several mG to sub-m G,measured by a flux-gate magnetometer.Consequently,the decay time of the Ramsey visibility is increased in the MI-ODT from 225(21)ms to 1150(24)ms.2.Determining the corresponding parameters of the MI-ODT for 85Rb qubit for the first time.Here,we first determine the corresponding coefficients of ?1.?2 and ?4 for 85Rb atoms under the condition of A=0.998(2)for wavelength of 830 nm.Subsequently,we study the behavior of tunability of dependence of magic intensity UM on the B fields for 85Rb qubits by tuning the values of A.And then we study and analyze the accompanying dephasing factors of 85Rb qubits in an elliptically polarized MI ODT.Furthermore,we study the coherent characteristic of 85Rb qubits in such a polarization-mediated MI ODT.And we reveal that the noise of the elliptic polarization causes dephasing effect on the 85Rb qubits but it could be efficiently mitigated by choosing the dynamical range of active polarization device.We also show that light shifts seen by qubits in an elliptically polarized MI-ODT can be more efficiently compensated due to the decrease in the ground state hyperpolarizability.3.Constructing a dual 3×3 MI-ODT array and demonstrating that the coherence times of the mixed-species qubits are both substantially enhanced and balanced.This mixed-species magic trapping technique relies on the tunability of the coefficient of the third-order cross term and ground state hyperpolarizability,which are inherently dependent on the degree of circular polarization of the trap laser.Experimentally,polarization of the ODT array for 85Rb qubits is finely adjusted to a definite value so that its working magnetic field required for magic trapping amounts to the one required for magically trapping 87Rb qubits in another ODT array with fully circular polarization.Ultimately,in such a polarization-mediated MI-ODT array,the coherence times of 87Rb and 85Rb qubits are respectively enhanced up to 891±47 ms and 943±35 ms.It is anticipated that the novel mixed-species MI-ODT array is a versatile platform for building scalable quantum computers with neutral atoms.