The transfer of quantum entangled states is of fundamental interest in quantum physics and plays an important role in quantum information processing, quantum communication, and quantum technology. Here, we propose a scheme to transfer quantum entangled states of two photonic qubits by utilizing four microwave cavities coupled to a superconducting qutrit (a three-level quantum system). The photonic qubits are encoded using two orthogonal eigenstates of the photon-number parity operator with eigenvalues ± 1, which allows for various encodings for the photonic qubits. The employment of four cavities at distinct frequencies effectively reduces the inter-cavity crosstalk. The utilization of only a single superconducting qutrit as the coupler significantly reduces the circuit resources. The entanglement transfer can be completed in just one step, making this scheme remarkably efficient. During the state transfer process, the third energy level of the coupler qutrit remains unoccupied, and thus decoherence from this level is diminished. Our numerical simulations demonstrate that within current circuit quantum electrodynamics technology, one can achieve high-fidelity transfer of the entangled states of two photonic qubits encoded via squeezed vacuum states and cat states. Our scheme possesses generality and can be applied to accomplish the same task in a variety of physical systems.
High-dimensional quantum systems, known as qudits with dimension
d>2, possess the capability to encode and process more information than traditional two-dimensional qubits. Entangled states serve as crucial resources for both quantum computation and quantum communication. On the basis of circuit quantum electrodynamics (QED) systems, we introduce an efficient scheme to deterministically generate high-dimensional multipartite entangled states of hybrid qutrits (
d=3). Assuming a simple initial state has already been prepared with the use of local operations, our method requires only a single step to produce hybrid Greenberger-Horne-Zeilinger (GHZ) entangled states among circuit QED systems consisting of superconducting qutrits and a superconducting cavity. Remarkably, the number of steps and the operational time remain constant as the number of qutrits increases, highlighting the efficiency and scalability of our approach. Using numerical simulations for a three-dimensional hybrid GHZ state of seven qutrits, we demonstrate the feasibility of our scheme and study the effects of various parameters on the fidelity. The importance of this research is in directing the experimental creation of multipartite, high-dimensional, and hybrid GHZ states, which can then be used to enhance quantum communication protocols and computational processes.
We propose a simple scheme for quantum state transfer between two qutrits in circuit quantum electrodynamics (QED). Other than the two qutrits, only one coupling cavity is adopted, and there is no requirement for a classical pulse or measurement. In the whole process, the cavity is virtually excited so that the decoherence caused by photon leakage of the cavity can be greatly suppressed. Numerical simulation shows that high fidelities (|
∼0.984| on average) can be achieved with present circuit QED technology, in which a low quality factor (|
Q≈4.1×104|) for the cavity has been adopted. Due to its simplicity, this scheme is quite general and can be applied to other quantum systems.