Coherent control for qubit state readout

TL;DR

This paper introduces a method using coherent control and electron wavepacket interference to improve hyperfine qubit state readout with broadband pulses, overcoming background scatter issues.

Contribution

It demonstrates a novel application of coherent control techniques to enable selective hyperfine qubit measurement with broadband pulses.

Findings

Achieved background-free atomic fluorescence for improved qubit detection

Enabled hyperfine qubit state readout using broadband pulses with interference techniques

Enhanced quantum state detection fidelity by over 100-fold

Abstract

Short pulses from mode-locked lasers can produce background-free atomic fluorescence by allowing temporal separation of the prompt incidental scatter from the subsequent atomic emission. We use this to improve quantum state detection of optical-frequency and electron-shelved trapped ion qubits by more than 2 orders of magnitude. For direct detection of qubits defined on atomic hyperfine structure, however, the large bandwidth of short pulses is greater than the hyperfine splitting, and repeated excitation is not qubit state selective. Here, we show that the state resolution needed for projective quantum measurement of hyperfine qubits can be recovered by applying techniques from coherent control to the orbiting valence electron of the queried ion. We demonstrate electron wavepacket interference to allow readout of the original qubit state using broadband pulses, even in the presence of large amounts of background laser scatter.