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Optics Continuum

Simulation of a two-qubit quantum gate based on classical transverse spatial waveguide mode encoding

Hongying Liu, Yue Zhang, Feng Xianing, Wei Lianfu

Published Aug 30, 2024• 0 citations
Publisher

Abstract

We demonstrate the simulation of a classical transverse mode-encoded controlled-NOT (CNOT) gate. Note that this integrated CNOT logic gate is composed of two 1/2 spatial mode beamsplitters and three 1/3 spatial mode beamsplitters, following the scheme proposed by Ralph. We will show how the CNOT gate can be analogously implemented by photonic integrated circuits in the classical regime, focusing on exploring the violation of Bell’s inequality by mode-entangled states. Our work may provide a promising approach to implementing small-scale quantum simulation and has the potential to enable practical and robust optical quantum information processing.

DOI
10.1364/optcon.527495

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We demonstrate the simulation of a classical transverse mode-encoded controlled-NOT (CNOT) gate. Note that this integrated CNOT logic gate is composed of two 1/2 spatial mode beamsplitters and three 1/3 spatial mode beamsplitters, following the scheme proposed by Ralph. We will show how the CNOT gate can be analogously implemented by photonic integrated circuits in the classical regime, focusing on exploring the violation of Bell’s inequality by mode-entangled states. Our work may provide a promising approach to implementing small-scale quantum simulation and has the potential to enable practical and robust optical quantum information processing.
As an important degree of freedom (d.o.f.) in photonic integrated circuits, the orthogonal transverse mode provides a promising and flexible way to increase communication capability, for both classical and quantum information processing. To construct large-scale on-chip multimode multi-d.o.f.s quantum systems, a transverse mode-encoded controlled-NOT (CNOT) gate is necessary. Here, with the help of our new transverse mode-dependent directional coupler and attenuator, we demonstrate the first multimode implementation of a 2-qubit quantum gate. The ability of the gate is demonstrated by entangling two separated transverse mode qubits with an average fidelity of 0.89±0.02 and the achievement of 10 standard deviations of violations in the quantum nonlocality verification. In addition, a fidelity of 0.82±0.01 is obtained from quantum process tomography used to completely characterize the CNOT gate. Our work paves the way for universal transverse mode-encoded quantum operations and large-scale multimode multi-d.o.f.s quantum systems.
Integrated quantum optics has the potential to markedly reduce the footprint and resource requirements of quantum information processing systems, but its practical implementation demands broader utilization of the available degrees of freedom within the optical field. To date, integrated photonic quantum systems have primarily relied on path encoding. However, in the classical regime, the transverse spatial modes of a multi-mode waveguide have been easily manipulated using the waveguide geometry to densely encode information. Here, we demonstrate quantum interference between the transverse spatial modes within a single multi-mode waveguide using quantum circuit-building blocks. This work shows that spatial modes can be controlled to an unprecedented level and have the potential to enable practical and robust quantum information processing.
To build universal quantum computers, an essential step is to realize the so-called controlled-NOT (CNOT) gate. Quantum photonic integrated circuits are well recognized as an attractive technology offering great promise for achieving large-scale quantum information processing, due to the potential for high fidelity, high efficiency, and compact footprints. Here, we demonstrate a supercompact integrated quantum CNOT gate on silicon by using the concept of symmetry breaking of a six-channel waveguide superlattice. The present path-encoded quantum CNOT gate is implemented with a footprint of $4.8\ifmmode\times\else\texttimes\fi{}4.45\text{ }\text{ }\ensuremath{\mu}{\mathrm{m}}^{2}$ ($\ensuremath{\sim}3\ensuremath{\lambda}\ifmmode\times\else\texttimes\fi{}3\ensuremath{\lambda}$) as well as a high-process fidelity of $\ensuremath{\sim}0.925$ and a low excess loss of <0.2  dB<0.2\text{ }\text{ }\mathrm{dB}<0.2  dB. The footprint is shrunk significantly by $\ensuremath{\sim}10\text{ }000$ times compared to those previous results based on dielectric waveguides. This offers the possibility of realizing practical large-scale quantum information processes and paving the way to the applications across fundamental science and quantum technologies.
Quantum networks provide a novel framework for quantum information processing, significantly improving system capacity through the interconnection of modular quantum nodes. Beyond the capability to distribute quantum states, the ability to remotely control quantum gates is a pivotal step for quantum networks. Here, we implement high-fidelity quantum controlled-not (cnot) gate teleportation with high-dimensional path encoded silicon photonic integrated circuits. Based on on-chip generation of the path-entangled quantum state, cnot gate operation, and chip-to-chip quantum photonic interconnect, the cnot gate is teleported between two remote quantum nodes connected by the single-mode optical fiber. Equip with 5 m (1 km)-long interconnecting fiber, quantum gate teleportation is verified by entangling remote qubits with 95.69%±1.19% (94.07%±1.54%) average fidelity and gate tomography with 94.81%±0.81% (93.04%±1.09%) fidelity. These results advance the realization of large-scale and practical quantum networks with photonic integrated circuits.
Optical qubits uniquely combine information transfer in optical fibres with a good processing capability and are therefore attractive tools for quantum technologies. A large challenge, however, is to overcome the low efficiency of two-qubit logic gates. The experimentally achieved efficiency in an optical controlled NOT (CNOT) gate reached approximately 11% in 2003 and has seen no increase since. Here we report on a new platform that was designed to surpass this long-standing record. The new scheme avoids inherently probabilistic protocols and, instead, combines aspects of two established quantum nonlinear systems: atom-cavity systems and Rydberg electromagnetically induced transparency (EIT). We demonstrate a CNOT gate between two optical photons with an efficiency of 41.7(4)% at a postselected process fidelity of 79(2)%. Moreover, we extended the scheme to a CNOT gate with multiple target qubits and produce entangled states of presently up to 5 photons. All these achievements are promising and have the potential to advance optical quantum information processing in which almost all advanced protocols would profit from high-efficiency logic gates.
Abstract We consider a theoretical model of a quantum node that implements a two-qubit controlled-NOT (CNOT) operation on photonic qubits with spatial encoding. Each of the qubits is represented by a pair of modes that support an arbitrary superposition of single-photon states. The active element of the node is a single or double quantum dot (QD) with a tunable frequency, coherently exchanging an energy quantum with the modes. The spectral characteristics of the elements of the quantum node are simulated. The probability of performing a controlled inversion of the qubit state is calculated, depending on the system parameters.