Modal and Polarization Qubits in Ti:LiNbO$_3$ Photonic Circuits for a Universal Quantum Logic Gate

TL;DR

This paper demonstrates the design and simulation of integrated lithium niobate photonic circuits capable of manipulating modal and polarization qubits, including a deterministic CNOT gate, for scalable quantum information processing.

Contribution

It introduces new integrated photonic components for modal and polarization qubits and presents a design for a deterministic two-qubit CNOT gate on a single chip.

Findings

Numerical simulations confirm the performance of the components.

Dispersion effects can be mitigated with an additional path.

The design leverages LiNbO₃'s polarization sensitivity for quantum operations.

Abstract

Lithium niobate photonic circuits have the salutary property of permitting the generation, transmission, and processing of photons to be accommodated on a single chip. Compact photonic circuits such as these, with multiple components integrated on a single chip, are crucial for efficiently implementing quantum information processing schemes. We present a set of basic transformations that are useful for manipulating modal qubits in Ti:LiNbO$_3$ photonic quantum circuits. These include the mode analyzer, a device that separates the even and odd components of a state into two separate spatial paths; the mode rotator, which rotates the state by an angle in mode space; and modal Pauli spin operators that effect related operations. We also describe the design of a deterministic, two-qubit, single-photon, CNOT gate, a key element in certain sets of universal quantum logic gates. It is implemented as a Ti:LiNbO$_3$ photonic quantum circuit in which the polarization and mode number of a single photon serve as the control and target qubits, respectively. It is shown that the effects of dispersion in the CNOT circuit can be mitigated by augmenting it with an additional path. The performance of all of these components are confirmed by numerical simulations. The implementation of these transformations relies on selective and controllable power coupling among single- and two-mode waveguides, as well as the polarization sensitivity of the Pockels coefficients in LiNbO$_3$.