Mid-circuit correction of correlated phase errors using an array of spectator qubits

Abstract

Scaling up invariably error-prone quantum processors is a formidable challenge. Although quantum error correction ultimately promises fault-tolerant operation, the required qubit overhead and error thresholds are daunting. In a complementary proposal, colocated, auxiliary “spectator” qubits act as in situ probes of noise and enable real-time, coherent corrections of data qubit errors. We used an array of cesium spectator qubits to correct correlated phase errors on an array of rubidium data qubits. By combining in-sequence readout, data processing, and feedforward operations, these correlated errors were suppressed within the execution of the quantum circuit. The protocol is broadly applicable to quantum information platforms and establishes key tools for scaling neutral-atom quantum processors: mid-circuit readout of atom arrays, real-time processing and feedforward, and coherent mid-circuit reloading of atomic qubits. Description Editor’s summary Qubits, the quantum information version of bits, are prone to decoherence as a consequence of their interaction with the environment. One way to manage decoherence is to correct for its effects. Recently, a scheme was proposed in which so-called “spectator” qubits are embedded in the system and used to read out the accumulated noise. This information is then used in real time to counter the decoherence of the “data” qubits that are performing the computation. Singh et al. implemented this proposal experimentally in a two-species system of neutral atoms placed in optical tweezers. The researchers demonstrated the success of the procedure by mitigating the effects of injected magnetic field noise. —Jelena Stajic An interspersed array of Cs and Rb atoms was used to implement a protocol for the correction of correlated errors.