Spectroscopy of low-frequency noise and its temperature dependence in a superconducting qubit

Yan, Fei; Bylander, Jonas; Gustavsson, Simon; Yoshihara, Fumiki; Harrabi, K.; Cory, David G.; Orlando, Terry P.; Nakamura, Y.; Tsai, Jaw Shen; Oliver, William

doi:10.1103/physrevb.85.174521

Cited by 74 publications

(86 citation statements)

References 30 publications

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“…The monotonic dependence of τ d on the correlation coefficient r c of the 2-qubit noises provides a much needed tool for measuring noise correlations. Since the Ramsey fringe measurement is much faster than the conventional two-point correlation measurement [27,30], Eq. (11) may provide a fast method for identifying the primary sources of noises in complex quantum circuits.…”

Section: Prl 116 010501 (2016) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

“…The dephasing times T Ã 2 are 173 AE 2, 177 AE 1, and 176 AE 2 ns by fitting to ln½P 1 ðτÞ ∝ −τ=2T 1 − ðτ=T Ã 2 Þ 2 , where P 1 is the j1i-state probability in the Ramsey fringe experiment [26]. Since three qubits have similar T Ã 2 values, we expect that the noise power spectral densities S j ðωÞ (j ¼ 1, 2, and 3), which characterize the flux-noise environments of these qubits, are approximately at the same level [26][27][28].…”

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confidence: 99%

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Suppression of Dephasing by Qubit Motion in Superconducting Circuits

Averin

Zhong

et al. 2016

Phys. Rev. Lett.

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We suggest and demonstrate a protocol which suppresses the low-frequency dephasing by qubit motion, i.e., transfer of the logical qubit of information in a system of n ≥ 2 physical qubits. The protocol requires only the nearest-neighbor coupling and is applicable to different qubit structures. Our analysis of its effectiveness against noises with arbitrary correlations, together with experiments using up to three superconducting qubits, shows that for the realistic uncorrelated noises, qubit motion increases the dephasing time of the logical qubit as ffiffiffi n p . In general, the protocol provides a diagnostic tool for measurements of the noise correlations. DOI: 10.1103/PhysRevLett.116.010501 Development of superconducting qubits [1][2][3][4][5][6][7] has reached the stage where it is interesting to discuss possible architectures of the quantum information processing circuits. The common feature of any quantum computation process of even moderate complexity is the requirement of information transfer between different elements of the qubit circuit. The most straightforward way of achieving this transfer is to physically move the quantum states representing the qubits of information along the circuit. In the case of superconducting qubits, potential for such a direct motion of logical qubits is offered by so-called negative-inductance SQUIDs [8,9], but operation of these circuits in the quantum regime [10] still needs to be demonstrated experimentally. Another method of transferring logical qubits between different physical qubits, already developed in experiments and adopted in this work, is based on creating controlled qubit-qubit interaction through coupling to a common resonator bus [5,[11][12][13]] (see Fig. 1). The goal of this Letter is to demonstrate that, in addition to its main function, the transfer of information between different circuit elements designed to perform different functions has an additional notable benefit: suppression of the low-frequency dephasing. We also show that it can be used to measure the noise correlations and, in this way, diagnose the primary sources of the noises.The basic mechanism of the noise suppression by qubit motion relies on the fact that the low-frequency noise is typically produced by fluctuators-see, e.g., Refs. [14,15] -in the form of impurity charges or magnetic moments, localized in each individual physical qubit, and, therefore, is not correlated among them. Motion of a logical qubit between different physical qubits limits the correlation time of the effective noise seen by this qubit and, therefore, suppresses its decoherence rate. This effect is qualitatively similar to the motional narrowing of the NMR lines [16], with the main difference that it is based on the controlled transfer of the qubit state, not random thermal motion as in NMR. Our protocol also has some similarities to the dynamic decoupling schemes-see, e.g., Refs. [17,18]where the qubit-noise interaction is suppressed by changing the qubit state in the effectively constant noise, while th...

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Section: Prl 116 010501 (2016) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

mentioning

confidence: 99%

Suppression of Dephasing by Qubit Motion in Superconducting Circuits

Averin

Zhong

et al. 2016

Phys. Rev. Lett.

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“…It is possible that other fabrication methods will yield devices with extremely low T c , so that T T c ; in this case D will be independent of T and our model leads to flux noise that does not change with temperature, as observed in another recent experiment. 6 In other samples T c may be higher, leading to additional T -dependence in the T ≈ T c regime [χ = χ 0 in Eq. (9)], where spin-clusters are present as was claimed in Ref.…”

Section: Interpretation Of the Experiment: Proximity To A Phase Tmentioning

confidence: 99%

Evidence for temperature-dependent spin diffusion as a mechanism of intrinsic flux noise in SQUIDs

et al. 2014

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The intrinsic flux noise observed in superconducting quantum interference devices (SQUIDs) is thought to be due to the fluctuation of electron spin impurities, but the frequency and temperature dependence observed in experiments do not agree with the usual 1/f models. We present theoretical calculations and experimental measurements of flux noise in rf-SQUID flux qubits that show how these observations, and previous reported measurements, can be interpreted in terms of a spindiffusion constant that increases with temperature. We fit measurements of flux noise in sixteen devices, taken in the 20 − 80 mK temperature range, to the spin-diffusion model. This allowed us to extract the spin-diffusion constant and its temperature dependence, suggesting that the spin system is close to a spin-glass phase transition.

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“…Flux noise has been investigated for decades to improve stability and sensitivity in superconducting flux-based devices. Its power spectral density (PSD) has been studied in superconducting quantum interference devices (SQUIDs) [1,2] and in various types of superconducting qubits, such as charge [3], flux [4][5][6][7][8][9][10], and phase qubits [11][12][13][14]. The spectra typically follow 1/f frequency dependence with a spectral density of 1-10 μ 0 / √ Hz at 1 Hz, where 0 = h/2e is the superconducting flux quantum.…”

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confidence: 99%

Flux qubit noise spectroscopy using Rabi oscillations under strong driving conditions

et al. 2014

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We infer the high-frequency flux noise spectrum in a superconducting flux qubit by studying the decay of Rabi oscillations under strong driving conditions. The large anharmonicity of the qubit and its strong inductive coupling to a microwave line enabled high-amplitude driving without causing significant additional decoherence. Rabi frequencies up to 1.7 GHz were achieved, approaching the qubit's level splitting of 4.8 GHz, a regime where the rotating-wave approximation breaks down as a model for the driven dynamics. The spectral density of flux noise observed in the wide frequency range decreases with increasing frequency up to 300 MHz, where the spectral density is not very far from the extrapolation of the 1/f spectrum obtained from the free-induction-decay measurements. We discuss a possible origin of the flux noise due to surface electron spins. Flux noise has been investigated for decades to improve stability and sensitivity in superconducting flux-based devices. Its power spectral density (PSD) has been studied in superconducting quantum interference devices (SQUIDs) [1,2] and in various types of superconducting qubits, such as charge [3], flux [4][5][6][7][8][9][10], and phase qubits [11][12][13][14]. The spectra typically follow 1/f frequency dependence with a spectral density of 1-10 μ 0 / √ Hz at 1 Hz, where 0 = h/2e is the superconducting flux quantum. The accessible frequency range of the PSD was limited to approximately 10 MHz in spin-echo measurements [4,5,9,15] and was extended to a few tens of megahertz using Carr-Purcell-Meiboom-Gill pulse sequences [9]. Recently, spin-locking measurements provided the PSD up to approximately 100 MHz [16], and a study of qubit relaxation due to dressed dephasing in a driven resonator revealed the PSD at approximately 1 GHz [17]. The spectrum in a higher-frequency range would give further information for better understanding of the microscopic origin of the flux fluctuations.Decay of Rabi oscillations has also been used as a tool to characterize the decoherence in superconducting qubits. PSDs of fluctuating parameters, such as charge, flux, or coupling strength to an external two-level system, at the Rabi frequency R can be detected [3,9,18,19]. The Rabi frequency is proportional to the amplitude of the driving field for weak to moderate driving at the qubit transition frequency, and Rabi frequencies in the gigahertz range have been achieved under a strong driving field [20][21][22]. However, the decay was not systematically studied because of the presence of extrinsic decoherence mechanisms under the strong driving conditions.To induce fast Rabi oscillations without significant extra decoherence, we choose a flux qubit having strong inductive coupling to a microwave line and large anharmonicity, * fumiki.yoshihara@riken.jp |(ω 12 − ω 01 )/ω 01 |, to avoid unwanted excitations to the higher energy levels, where ω ij is the transition frequency between the |i and |j states. We measured Rabi oscillations in a wide range of R /2π from 2.7 MHz to 1.7 GHz and evaluat...

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Spectroscopy of low-frequency noise and its temperature dependence in a superconducting qubit

Cited by 74 publications

References 30 publications

Suppression of Dephasing by Qubit Motion in Superconducting Circuits

Suppression of Dephasing by Qubit Motion in Superconducting Circuits

Evidence for temperature-dependent spin diffusion as a mechanism of intrinsic flux noise in SQUIDs

Flux qubit noise spectroscopy using Rabi oscillations under strong driving conditions

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