Decoherence in Josephson-Junction Qubits due to Critical Current Fluctuations

By D. Harlingen, T. Robertson, B. Plourde, P. A. Reichardt, Trevis A. Crane, John Clarke. 2004

151 citations recorded by the source corpus.

We compute the decoherence caused by $1∕f$ fluctuations at low frequency $f$ in the critical current ${I}_{0}$ of Josephson junctions incorporated into flux, phase, charge, and hybrid flux-charge superconducting quantum bits (qubits). The dephasing time ${\ensuremath{\tau}}_{\ensuremath{\phi}}$ scales as ${I}_{0}∕\ensuremath{\Omega}\ensuremath{\Lambda}{S}_{{I}_{0}}^{1∕2}(1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz})$, where $\ensuremath{\Omega}∕2\ensuremath{\pi}$ is the energy-level splitting frequency, ${S}_{{I}_{0}}(1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz})$ is the spectral density of the critical-current noise at $1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$, and $\ensuremath{\Lambda}\ensuremath{\equiv}\ensuremath{\mid}{I}_{0}d\ensuremath{\Omega}∕\ensuremath{\Omega}d{I}_{0}\ensuremath{\mid}$ is a parameter computed for given parameters for each type of qubit that specifies the sensitivity of the level splitting to critical-current fluctuations. Computer simulations show that the envelope of the coherent oscillations of any qubit after time $t$ scales as $\mathrm{exp}(\ensuremath{-}{t}^{2}∕2{\ensuremath{\tau}}_{\ensuremath{\phi}}^{2})$ when the dephasing due to critical-current noise dominates the dephasing from all sources of dissipation. We compile published results for fluctuations in the critical current of Josephson tunnel junctions fabricated with different technologies and a wide range in ${I}_{0}$ and area $\mathcal{A}$, and show that their values of ${S}_{{I}_{0}}(1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz})$ scale to within a factor of 3 of $[144{({I}_{0}∕\ensuremath{\mu}\mathrm{A})}^{2}∕(\mathcal{A}∕\ensuremath{\mu}{\mathrm{m}}^{2})]{(\mathrm{pA})}^{2}∕\mathrm{Hz}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We empirically extrapolate ${S}_{{I}_{0}}^{1∕2}(1\phantom{\rule{0.3em}{0ex}}\mathrm{Hz})$ to lower temperatures using a scaling $T(\mathrm{K})∕4.2$. Using this result, we find that the predicted values of ${\ensuremath{\tau}}_{\ensuremath{\phi}}$ at $100\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ range from $0.8\phantom{\rule{0.5em}{0ex}}\text{to}\phantom{\rule{0.5em}{0ex}}12\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$, and are usually substantially longer than values measured experimentally at lower temperatures.

Subfields: Atomic and Molecular Physics, and Optics, Condensed Matter Physics

View Paper: https://www.semanticscholar.org/paper/2c92f99ea6c95d52f48711a59cb7c238e91f00af

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In Atomic and Molecular Physics, and Optics

In Condensed Matter Physics

Citations in the corpus

Nano Superconducting Quantum Interference device: a powerful tool for nanoscale investigations (2015, background): “ons 20 such as biomagnetism, geophysics and quantum computing. In particular, concerning the latter topic, it seems that the low frequency noise is related to the decoherence time in Josephson qubits [53,54]. This has stimulated many theoretical [55, 56, 57] and experimental [58, 59, 60, 61, 62] inv”
Noise spectroscopy through dynamical decoupling with a superconducting flux qubit (2011, methodology): “Despite observing levels of 1/ f flux and critical-current noise similar to those observed ubiquitously in superconducting qubits and SQUID”
Superconducting quantum bits (2008, background): “The first is critical-current fluctuations, which arise from fluctuations in the transparency of the junction caused by the trapping and untrapping of electrons in the tunnel barrie”
1 / f noise: Implications for solid-state quantum information (2013, methodology): “…as I0 ≡ ΩΛS1/2I0 (1 Hz), where SI0(1 Hz) is the spectral density of the critical-current noise at 1 Hz, and Λ = I0dΩ/ΩdI0 is computed for given parameters for each type of qubit that specifies the sensitivity of the level splitting to critical-current fluctuations (Van Harlingen et al., 2004).”
Dynamical decoupling and noise spectroscopy with a superconducting flux qubit (2011, background): “Despite observing levels of 1/f flux and critical-current noise similar to those observed ubiquitously in superconducting qubits and SQUIDs [6, 29], we could mitigate this noise dynamically to increase the pure dephasing times beyond”