Implementation of quantum phase gate between two atoms via Rydberg antiblockade and adiabatic passage

Combining adiabatic passage and Rydberg antiblockade, we propose a scheme to implement a two-qubit phase gate between two Rydberg atoms. Detuning parameters between frequencies of atomic transitions and those of the corresponding driving lasers are carefully chosen to offset the blockade effect of two Rydberg atoms, so that an effective Hamiltonian,representing a single-photon detuning L-type three-level system and concluding the quantum state of two Rydberg atoms excited simultaneously, is obtained. The adiabatic-passage technique, based on the effective Hamiltonian, is adopted to implement a two-atom phase gate by using two time-dependent Rabi frequencies. Numerical simulations indicate that a high-fidelity two-qubit p-phase gate is constructed and its operation time does not have to be controlled accurately. Besides,owing to the long coherence time of the Rydberg state, the phase gate is robust against atomic spontaneous emission.

Selective enhancement of green upconversion luminescence of Er-Yb:NaYF4 by surface plasmon resonance of W18O49 nanoflowers and applications in temperature sensing

The W（18）O（49） nanoflowers with a diameter of 500 nm are prepared by a facile hydrothermal method. The Er-Yb：NaYF4 nanoparticles are adsorbed on the petals（the position of the strongest local electric field on W（18）O（49） nanoflowers）.With a 976 nm laser diode（LD） as an excitation source, the selectively green upconversion luminescence（UCL） is observed to be enhanced by two orders of magnitude in Er-Yb： NaYF4/W（18）O（49） nanoflowers heterostructures. It suggests that the near infrared（NIR）-excited localized surface plasmon resonance（LSPR） of W（18）O（49） is primarily responsible for the enhanced UCL, which could be partly reabsorbed by the W（18）O（49）, thus leading to the selective enhancement of green UCL for the Er-Yb： NaYF4. The fluorescence intensity ratio is investigated as a function of temperature based on the intense green UCL, which indicates that Er-Yb： NaYF4/W（18）O（49） nanoflower heterostructures have good potential for developing into temperature sensors.

Quantum parametric amplification of phonon-mediated magnon-spin interaction

The recently developed hybrid magnonics provides new opportunities for advances in both the study of magnetism and the development of quantum information processing.However,engineering coherent quantum state transfer between magnons and specific information carriers,in particular,mechanical oscillators and solid-state spins,remains challenging due to the intrinsically weak interactions and the frequency mismatch between different components.Here,we show how to strongly couple the magnon modes in a nanomagnet to the quantized mechanical motion(phonons)of a micromechanical cantilever in a hybrid tripartite system.The coherent and enhanced magnon-phonon coupling is engineered by introducing the quantum parametric amplification of the mechanical motion.With experimentally feasible parameters,we show that the mechanical parametric drive can be adjusted to drive the system into the strong-coupling regime and even the ultrastrong-coupling regime.Furthermore,we show the coherent state transfer between the nanomagnet and a nitrogen-vacancy center in the dispersive-coupling regime,with the magnon-spin interaction mediated by the virtually-excited squeezed phonons.The amplified mechanical noise can hardly interrupt the coherent dynamics of the system even for low mechanical quality factors,which removes the requirement of applying additional engineered-reservoir techniques.Our work opens up prospects for developing novel quantum transducers,quantum memories and high-precision measurements.

Robust beam splitter with fast quantum state transfer through a topological interface

The Su–Schrieffer–Heeger(SSH)model,commonly used for robust state transfers through topologically protected edge pumping,has been generalized and exploited to engineer diverse functional quantum devices.Here,we propose to realize a fast topological beam splitter based on a generalized SSH model by accelerating the quantum state transfer(QST)process essentially limited by adiabatic requirements.The scheme involves delicate orchestration of the instantaneous energy spectrum through exponential modulation of nearest neighbor coupling strengths and onsite energies,yielding a significantly accelerated beam splitting process.Due to properties of topological pumping and accelerated QST,the beam splitter exhibits strong robustness against parameter disorders and losses of system.In addition,the model demonstrates good scalability and can be extended to two-dimensional crossed-chain structures to realize a topological router with variable numbers of output ports.Our work provides practical prospects for fast and robust topological QST in feasible quantum devices in large-scale quantum information processing.

Fast topological pumping for the generation of large-scale Greenberger–Horne–Zeilinger states in a superconducting circuit

Topological pumping of edge states in the finite lattice with nontrivial topological phases provides a powerful means for robust excitation transfer,requiring extremely slow evolution to follow an adiabatic transfer.Here,we propose fast topological pumping via edge channels to generate large-scale Greenberger–Horne–Zeilinger(GHZ)states in a topological superconducting circuit with a sped-up evolution process.The scheme indicates a conceptual way of designing fast topological pumping related to the instantaneous energy spectrum characteristics rather than relying on the shortcuts to adiabaticity.Based on fast topological pumping,large-scale GHZ states show greater robustness against on-site potential defects,the fluctuation of couplings and losses of the system in comparison with the conventional adiabatic topological pumping.With experimentally feasible qutrit-resonator coupling strengths and moderate decay rates of qutrits and resonators,fast topological pumping drastically improves the scalability of GHZ states with a high fidelity.Our work opens up prospects for the realization of large-scale GHZ states based on fast topological pumping in the superconducting quantum circuit system,which provides potential applications of topological matters in quantum information processing.

Unselective ground-state blockade of Rydberg atoms for implementing quantum gates

A dynamics regime of Rydberg atoms,unselective ground-state blockade(UGSB),is proposed in the context of Rydberg antiblockade(RAB),where the evolution of two atoms is suppressed when they populate in an identical ground state.UGSB is used to implement a SWAP gate in one step without individual addressing of atoms.Aiming at circumventing common issues in RAB-based gates including atomic decay,Doppler dephasing,and fluctuations in the interatomic coupling strength,we modify the RAB condition to achieve a dynamical SWAP gate whose robustness is much greater than that of the nonadiabatic holonomic one in the conventional RAB regime.In addition,on the basis of the proposed SWAP gates,we further investigate the implementation of a three-atom Fredkin gate by combining Rydberg blockade and RAB.The present work may facilitate to implement the RAB-based gates of strongly coupled atoms in experiment.

One-step implementation of Rydberg-antiblockade SWAP and controlled-SWAP gates with modified robustness

The prevalent fashion of executing Rydberg-mediated two-and multi-qubit quantum gates in neutral atomic systems is to pump Rydberg excitations using multistep piecewise pulses in the Rydberg blockade regime.Here, we propose to synthesize a Λ-type Rydberg antiblockade(RAB) of two neutral atoms using periodic fields,which facilitates one-step implementations of SWAP and controlled-SWAP(CSWAP) gates with the same gate time. Besides, the RAB condition is modified so as to circumvent the sensitivity of RAB-based gates to infidelity factors, including atomic decay, motional dephasing, and interatomic distance deviation. Our work makes up the absence of one-step schemes of Rydberg-mediated SWAP and CSWAP gates and may pave a way to enhance the robustness of RAB-based gates.