Demonstrating Heisenberg-limited unambiguous phase estimation without adaptive measurements

TL;DR

This paper presents a non-adaptive interferometric scheme achieving Heisenberg-limited phase estimation, resolving phase ambiguity, and demonstrating practical advantages over adaptive methods in quantum metrology.

Contribution

The authors introduce a non-adaptive, experimentally feasible scheme for Heisenberg-limited phase estimation that simplifies implementation and resolves phase ambiguity without prior knowledge.

Findings

Achieved Heisenberg-limited phase estimation without adaptive measurements.

Resolved phase ambiguity with multiple phase shift applications.

Demonstrated surpassing the standard quantum limit with a simplified adaptive scheme.

Abstract

We derive, and experimentally demonstrate, an interferometric scheme for unambiguous phase estimation with precision scaling at the Heisenberg limit that does not require adaptive measurements. That is, with no prior knowledge of the phase, we can obtain an estimate of the phase with a standard deviation that is only a small constant factor larger than the minimum physically allowed value. Our scheme resolves the phase ambiguity that exists when multiple passes through a phase shift, or NOON states, are used to obtain improved phase resolution. Like a recently introduced adaptive technique [Higgins et al 2007 Nature 450 393], our experiment uses multiple applications of the phase shift on single photons. By not requiring adaptive measurements, but rather using a predetermined measurement sequence, the present scheme is both conceptually simpler and significantly easier to implement. Additionally, we demonstrate a simplified adaptive scheme that also surpasses the standard quantum limit for single passes.