State transfer and entanglement between two-and four-level atoms in a cavity

Qudits with a large Hilbert space to host quantum information are widely utilized in various applications, such as quantum simulation and quantum computation, but the manipulation and scalability of qudits still face challenges. Here, we propose a scheme to directly and locally transfer quantum information from multiple atomic qubits to a single qudit and vice versa in an optical cavity. With the qubit–qudit interaction induced by the cavity, our scheme can transfer quantum states efficiently and measurement-independently. In addition, this scheme can robustly generate a high-dimensional maximal entangled state with asymmetric particle numbers, showing its potential in realizing an entanglement channel. Such an information interface for qubits and qudit may have enlightening significance for future research on quantum systems in hybrid dimensions.

Experimental demonstration of a fast calibration method for integrated photonic circuits with cascaded phase shifters

With the development of research on integrated photonic quantum information processing,the integration level of the integrated quantum photonic circuits has been increasing continuously,which makes the calibration of the phase shifters on the chip increasingly difficult.For the calibration of multiple cascaded phase shifters that is not easy to be decoupled,the resources consumed by conventional brute force methods increase exponentially with the number of phase shifters,making it impossible to calibrate a relatively large number of cascaded phase shifters.In this work,we experimentally validate an efficient method for calibrating cascaded phase shifters that achieves an exponential increase in calibration efficiency compared to the conventional method,thus solving the calibration problem for multiple cascaded phase shifters.Specifically,we experimentally calibrate an integrated quantum photonic circuit with nine cascaded phase shifters and achieve a high-precision calibration with an average fidelity of 99.26%.

Quantum information transfer between a two-level and a four-level quantum systems

Quantum mechanics provides a disembodied way to transfer quantum information from one quantum object to another.In theory,this quantum information transfer can occur between quantum objects of any dimension,yet the reported experiments of quantum information transfer to date have mainly focused on the cases where the quantum objects have the same dimension.Here,we theoretically propose and experimentally demonstrate a scheme for quantum information transfer between quantum objects of different dimensions.By using an optical qubit-ququart entangling gate,we observe the transfer of quantum information between two photons with different dimensions,including the flow of quantum information from a four-dimensional photon to a twodimensional photon and vice versa.The fidelities of the quantum information transfer range from 0.700 to 0.917,all above the classical limit of 2/3.Our work sheds light on a new direction for quantum information transfer and demonstrates our ability to implement entangling operations beyond two-level quantum systems.

Steering paradox for Einstein–Podolsky–Rosen argument and its extended inequality

The Einstein–Podolsky–Rosen(EPR)paradox is one of the milestones in quantum foundations,arising from the lack of a local realistic description of quantum mechanics.The EPR paradox has stimulated an important concept of“quantum nonlocality,”which manifests itself in three types:quantum entanglement,quantum steering,and Bell’s nonlocality.Although Bell’s nonlocality is more often used to show“quantum nonlocality,”the original EPR paradox is essentially a steering paradox.In this work,we formulate the original EPR steering paradox into a contradiction equality,thus making it amenable to experimental verification.We perform an experimental test of the steering paradox in a two-qubit scenario.Furthermore,by starting from the steering paradox,we generate a generalized linear steering inequality and transform this inequality into a mathematically equivalent form,which is friendlier for experimental implementation,i.e.,one may measure the observables only in the x,y,or z axis of the Bloch sphere,rather than other arbitrary directions.We also perform experiments to demonstrate this scheme.Within the experimental errors,the experimental results coincide with theoretical predictions.Our results deepen the understanding of quantum foundations and provide an efficient way to detect the steerability of quantum states.