Abstract
To build a quantum computing device, which is capable of generating arbitrary input states and performing universal unitary gate operations (UUGOs), is an important goal in the field of quantum information science. However, only a few special quantum computations have been reported by now based on specific input states and well-designed information processors. Here, we demonstrate a flexible scheme for two-qubit quantum computations by employing the polarization and the spatial mode of a single photon. Two-qubit UUGOs both in free-space optics and for arbitrary pure input states consisting of separable states and entangled states are presented. Quantum state tomography and process tomography are used to characterize the fidelity of the output states and the gate operations we considered. Beyond a demonstration, we believe that our work also enriches the techniques of bulk-optics for quantum information study and has a broad application for other fundamental research.
Highlights
A quantum computer has the potential for propelling the information society forward because it could efficiently deal with the problems intractable for a classical computer.1–7 As a fundamental expectation, a quantum computer should be capable of performing universal computation, meaning that it could manipulate arbitrary input states and implement universal unitary gate operations (UUGOs)
This work could contain more computational situations compared with the previous studies and contribute to the bulk-optics quantum technologies from the experimental aspect, like the realization of two-qubit UUGO based on the polarization and orbital angular momentum (OAM)
The above discussion is only focused on the flexible scheme with pure two-qubit input states and UUGO based on the polarization and spatial DOFs of a single photon
Summary
A quantum computer has the potential for propelling the information society forward because it could efficiently deal with the problems intractable for a classical computer. As a fundamental expectation, a quantum computer should be capable of performing universal computation, meaning that it could manipulate arbitrary input states and implement universal unitary gate operations (UUGOs). A quantum computer should be capable of performing universal computation, meaning that it could manipulate arbitrary input states and implement universal unitary gate operations (UUGOs). In Ref. 19, the UUGO have been realized by exploiting high-dimensional entanglement to reduce the number of entangling two-qubit gates, and arbitrary separate pure input states are produced. The UUGO scheme with arbitrary pure input states (APISs) consisting of separable and entangled states has not been discussed. UUGOs both in free-space optics and for APISs consisting of separable and entangled states have been realized. This work could contain more computational situations compared with the previous studies and contribute to the bulk-optics quantum technologies from the experimental aspect, like the realization of two-qubit UUGO based on the polarization and orbital angular momentum (OAM).. This work could contain more computational situations compared with the previous studies and contribute to the bulk-optics quantum technologies from the experimental aspect, like the realization of two-qubit UUGO based on the polarization and orbital angular momentum (OAM). The quantum computation platform we built can be used for other fundamental studies in the future, such as the diagnosis of an unknown two-qubit state, a two-qubit quantum approximate optimization algorithm, and efficient simulation of Szegedy directed quantum walks in free-space optics
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