Single-channel Hadamard gate through single-photon Raman Scattering in Chiral Quantum Nanophotonics

Hadamard gate (H-gate) is indispensable to constitute complete sets of logic gates for universal quantum computing. Practical implementations can be classified into atom- and photon-based. While atom-based techniques are rather mature by employing consecutive electromagnetic pulses to drive qubit rotations on Bloch sphere, it is of limited coherent time, and may not be compatible with photon-based quantum communication protocol in scalable quantum internet blueprint. Henceforth, photon-based implementations may play significant roles, which are typically realized by using linear optical elements. However, such schemes require different photonic channels to accommodate binary qubits, thus resulting in limited spatial utility.
To enhance spatial utility, we propose a novel single-channel H-gate scheme by chirally coupling Lambda-type atoms to 1D waveguide, and exploiting photon frequency degree of freedom as qubit. The underlying physics of gate operations here, is frequency conversion through single-photon Raman scattering. The single-channel feature enhances the spatial utility to be highly scalable. Such a scheme is readily feasible due to the advent of chiral coupling technique using photon spin-momentum locking and polarized dipole moment in quantum nanophotonics.