Superconducting antiqubits achieve optimal phase estimation via unitary inversion

TL;DR

This paper introduces 'antiqubits'—superconducting qubits simulated as positron-like particles—to achieve optimal phase estimation through unitary inversion, demonstrating theoretical and experimental quantum advantage in sensing applications.

Contribution

The work presents a novel platform-specific method for unitary inversion using antiqubits, enabling enhanced quantum sensing and phase estimation capabilities.

Findings

Antiqubits enable time-inversion of unitaries on superconducting qubits.

Entangled qubit-antiqubit pairs maximize Fisher information in field sensing.

Experimental validation confirms theoretical quantum advantage in phase estimation.

Abstract

A positron is equivalent to an electron traveling backward through time. Casting transmon superconducting qubits as akin to electrons, we simulate a positron with a transmon subject to particular resonant and off-resonant drives. We call positron-like transmons "antiqubits." An antiqubit's effective gyromagnetic ratio equals the negative of a qubit's. This fact enables us to time-invert a unitary implemented on a transmon by its environment. We apply this platform-specific unitary inversion, with qubit--antiqubit entanglement, to achieve a quantum advantage in phase estimation: consider measuring the strength of a field that points in an unknown direction. An entangled qubit--antiqubit sensor offers the greatest possible sensitivity (amount of Fisher information), per qubit, per application of the field. We prove this result theoretically and observe it experimentally. This work shows how antimatter, whether real or simulated, can enable platform-specific unitary inversion and benefit quantum information processing.