Multi-level quantum noise spectroscopy

Abstract

System noise identification is crucial to the engineering of robust quantum systems. Although existing quantum noise spectroscopy (QNS) protocols measure an aggregate amount of noise affecting a quantum system, they generally cannot distinguish between the underlying processes that contribute to it. Here, we propose and experimentally validate a spin-locking-based QNS protocol that exploits the multi-level energy structure of a superconducting qubit to achieve two notable advances. First, our protocol extends the spectral range of weakly anharmonic qubit spectrometers beyond the present limitations set by their lack of strong anharmonicity. Second, the additional information gained from probing the higher-excited levels enables us to identify and distinguish contributions from different underlying noise mechanisms.

Intrinsic and induced quantum quenches for enhancing qubit-based quantum noise spectroscopy

“…While this can be realized in many different experimental platforms (e.g., a superconducting transmon qubit, as implemented in Ref. 19 ), we focus here on sensor based on a S = 1 NV defect in diamond 22 . For this system, we discuss a specific protocol to reconstruct finite-frequency spectral function by engineering time-dependent quenches.…”

“…A key technique in quantum sensing is to use a suitably driven sensor qubit to characterize a noisy, dissipative environment. Commonly referred to as quantum noise spectroscopy (QNS) 1 , this modality allows one to understand and possibly mitigate sources of decoherence that degrade a quantum processor 2 – 19 . It also serves as a powerful means to probe a complicated many-body target system via its fluctuation properties (see, e.g., 20 – 24 ).…”

“…It also serves as a powerful means to probe a complicated many-body target system via its fluctuation properties (see, e.g., 20 – 24 ). While many QNS protocols focus on the more specific problem of characterizing classical Gaussian noise 4 – 12 , recent work has explored methods that go beyond these assumptions 13 – 19 , 25 – 30 .…”

All-optical noise spectroscopy of a solid-state spin

“…Noise spectroscopy elucidates the fundamental noise sources in spin systems, which is essential for developing spin qubits with long coherence times for quantum information processing [1], communication [2], and sensing [3]. But noise spectroscopy typically relies on microwave coherent spin control to extract the noise spectrum [4][5][6][7][8][9], which becomes infeasible when there are highfrequency noise components stronger than the available microwave power. Here, we demonstrate an alternative all-optical approach to performing noise spectroscopy.…”

“…The coherent control of spin qubits can be used to conduct noise spectroscopy of their surrounding environment [4][5][6][7][8][9], in which the spin is used to probe the frequencies of the fluctuating fields generated by neighbouring nuclear and electronic spins as well as the strength of their interaction with the spin (i.e., the spectral density). Such noise spectroscopy using microwave fields has shed light on the fundamental noise processes of spin systems such as superconducting qubits [4,5], nitrogen-vacancy centres in diamond [6,7], and gate-defined quantum dots [8,9]. However, the bandwidth of noise spectroscopy utilising microwave fields is limited by the rate of the spin rotation (i.e., the Rabi frequency), which must exceed the frequencies of the noise.…”