Lifetime and Coherence of Two-Level Defects in a Josephson Junction

Shalibo, Yoni; Rofe, Yaara; Shwa, David; Zeides, F.; Neeley, M.; Martinis, John M.; Katz, Nadav

doi:10.1103/physrevlett.105.177001

Cited by 97 publications

(119 citation statements)

References 18 publications

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“…Assuming an overall TLS density of 10 2 /(µm 3 GHz) 6,13 , this leads to the effective frequency density of TLS in the interaction region of a single TLS of ρ ∼ 10 −1 /GHz. We note that the density obtained in Refs.…”

Section: Effective Inter-tls Interaction Rangementioning

confidence: 99%

“…For coupling strengths that are much weaker than the individual decoherence rates of qubit and defect, the effect of the TLS on the qubit will be that of a strongly peaked high-frequency noise spectrum. In other experiments, strongly coupled coherent TLS are often found to cause avoided level crossings in superconducting circuits which include Josephson junctions 5,6 . Those TLS are believed to reside in the dielectric forming the tunnelling barrier inside the circuits Josephson junctions, enabling their stronger coupling to the circuit dynamics.…”

Section: Introductionmentioning

confidence: 99%

“…With the advent of highly coherent superconducting circuits for quantum applications, previously neglected sources of environmental noise become important. One such cause of decoherence are spurious two-level systems (TLS), which are believed to be present in large numbers in the amorphous dielectric oxide layer covering the superconducting films 5,6 . Ensembles of TLS naturally explain the low-temperature properties of glasses 7,8 and are used as a universal model for 1/f -type low-frequency noise in electric circuits 9,10 .…”

Section: Introductionmentioning

confidence: 99%

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Interacting two-level defects as sources of fluctuating high-frequency noise in superconducting circuits

et al. 2015

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Since the very first experiments, superconducting circuits have suffered from strong coupling to environmental noise, destroying quantum coherence and degrading performance. In state-of-the-art experiments, it is found that the relaxation time of superconducting qubits fluctuates as a function of time. We present measurements of such fluctuations in a 3D-Transmon circuit and develop a qualitative model based on interactions within a bath of background two-level systems (TLS) which emerge from defects in the device material. In our model, the time-dependent noise density acting on the qubit emerges from its near-resonant coupling to high-frequency TLS which experience energy fluctuations due to their interaction with thermally fluctuating TLS at low frequencies. We support the model by providing experimental evidence of such energy fluctuations observed in a single TLS in a phase qubit circuit.

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Section: Effective Inter-tls Interaction Rangementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Interacting two-level defects as sources of fluctuating high-frequency noise in superconducting circuits

et al. 2015

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“…[5][6][7][8][9][10][11][12] Since TLSs are ubiquitous in solid-state devices, [13][14][15] it is important to detect and investigate them in order to achieve better qubit performance. 6,16,17 In recent experiments on the mechanism and interaction of TLSs in superconducting qubits, TLSs are detected through the standard energy spectroscopy measurement. 20,21 With this traditional method, the coupling between a TLS and a qubit results in an anti-crossing (or energy level splitting) on spectroscopy.…”

mentioning

confidence: 99%

Rapid characterization of microscopic two-level systems using Landau-Zener transitions in a superconducting qubit

Tan

et al. 2015

Applied Physics Letters

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We demonstrate a fast method to detect microscopic two-level systems in a superconducting phase qubit. By monitoring the population leak after sweeping the qubit bias flux, we are able to measure the two-level systems that are coupled with the qubit. Compared with the traditional method that detects two-level systems by energy spectroscopy, our method is faster and more sensitive. This method supplies a useful tool to investigate two-level systems in solid-state qubits.

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“…This model is broadly applicable to potential quantum computing technologies [22] and reproduces also the dynamics of spurious two-level systems [23][24][25], a notorious source of decoherence for superconducting qubits.…”

mentioning

confidence: 99%

Efficient Estimation of Resonant Coupling between Quantum Systems

2014

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We present an efficient method for the characterization of two coupled discrete quantum systems, one of which can be controlled and measured. For two systems with transition frequencies ωq, ωr, and coupling strength g we show how to obtain estimates of g and ωr whose error decreases exponentially in the number of measurement shots rather than as a power law expected in simple approaches. Our algorithm can thereby identify g and ωr simultaneously with high precision in a few hundred measurement shots. This is achieved by adapting measurement settings upon data as it is collected. We also introduce a method to eliminate erroneous estimates with small overhead. Our algorithm is robust against the presence of relaxation and typical noise. Our results are applicable to many candidate technologies for quantum computation, in particular, for the characterization of spurious two-level systems in superconducting qubits or stripline resonators. Parameter estimation in many microscopic and some macroscopic systems inevitably involves quantum measurements. This implies that parameters cannot be identified with a single measurement shot since the outcome of such a measurement is generally random. Instead, the standard approach is to determine ensemble averages for many experiments and fit the parameters of certain quantitative models to those averages. The most common example for this is spectroscopy: it involves direct measurement of the energy splittings between quantum states in the form of resonances to incoming radiation. Typically, a large ensemble average is produced by gathering data from a large number of independent trials, either simultaneously on an ensemble of molecules (in nuclear magnetic resonance [1]) or from many repetitions of a specific experiment (in optical spectroscopy of single molecules, quantum dots, or superconducting qubits [2]).While being reliable in many contexts, this approach is often too resource intensive. Specifically, the error in the estimate of a single expectation value at a fixed measurement setting decreases in proportion to M − 1 2 r after M r measurement shots. Moreover, many choices of measurement settings are usually required for complex measurement tasks. Such slowness of parameter estimation can also turn into imprecision in the estimate if the parameters of interest drift as a function of time, broadening spectroscopic signatures.Imprecision in system characterization is particularly problematic for quantum information processing applications. These require extremely precise logic operations, usually implemented as pulses. The pulse parameters such as length, amplitude, and carrier frequency, depend on the system parameters. In manufactured solid state qubits, this is rather central as they are subject to fabrication uncertainty.In this Letter, we demonstrate that advanced spectroscopy can be performed far more efficiently. Our re-(b) (a) Figure 1: (color online) (a) Theoretically obtained swap spectrum in frequency-waiting time plane.Here, δ = (ωq − ωr,0)/(2g0), with ωq the q...

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Lifetime and Coherence of Two-Level Defects in a Josephson Junction

Cited by 97 publications

References 18 publications

Interacting two-level defects as sources of fluctuating high-frequency noise in superconducting circuits

Interacting two-level defects as sources of fluctuating high-frequency noise in superconducting circuits

Rapid characterization of microscopic two-level systems using Landau-Zener transitions in a superconducting qubit

Efficient Estimation of Resonant Coupling between Quantum Systems

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