Measuring effective temperatures of qubits using correlations

Abstract

Initialization of a qubit in a pure state is a prerequisite for quantum computer operation. Qubits are commonly initialized by cooling to their ground states through passive thermalization or by using active reset protocols. To accurately quantify the initialization one requires a tool to measure the excited state population with sufficient accuracy given that the spurious excited state population may not exceed a fraction of a percent. In this Letter we propose a new technique of finding the excited state population of a qubit using correlations between two sequential measurements. We experimentally implement the proposed technique using a circuit QED platform and compare its performance with previously developed techniques. Unlike other techniques, our method does not require high-fidelity readout and does not involve the excited levels of the system outside of the qubit subspace. We experimentally demonstrated measurement of the spurious qubit population with accuracy of up to $0.01\%$. This accuracy enabled us to perform "temperature spectroscopy" of the qubit which helps to shed light on sources of the decoherence.

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Cited by in corpus (15)

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• Quasiparticles in superconducting qubits with asymmetric junctions
• Approaching Heisenberg-scalable thermometry with built-in robustness against noise
• Primary thermometry of propagating microwaves in the quantum regime
• Quantum bath suppression in a superconducting circuit by immersion cooling
• Acceptor-induced bulk dielectric loss in superconducting circuits on silicon
• Thermometry Based on a Superconducting Qubit
• Markovian Noise Modelling and Parameter Extraction Framework for Quantum Devices
• Applications of Superconductor-Normal Metal Interfaces
• Estimating the Energy Threshold of Phonon-mediated Superconducting Qubit Detectors Operated in an Energy-Relaxation Sensing Scheme
• Testing spontaneous wavefunction collapse with quantum electromechanics
• Leveraging collective effects for thermometry in waveguide quantum electrodynamics
• Dynamic phases induced by two-level system defects on driven qubits
• Effects of the thin-film thickness on superconducting NbTi microwave resonators for on-chip cryogenic thermometry
• Protocol for temperature sensing using a three-level transmon circuit