6 research outputs found
Engineering Dynamical Sweet Spots to Protect Qubits from 1/ Noise
Protecting superconducting qubits from low-frequency noise is essential for
advancing superconducting quantum computation. Based on the application of a
periodic drive field, we develop a protocol for engineering dynamical sweet
spots which reduce the susceptibility of a qubit to low-frequency noise. Using
the framework of Floquet theory, we prove rigorously that there are manifolds
of dynamical sweet spots marked by extrema in the quasi-energy differences of
the driven qubit. In particular, for the example of fluxonium biased slightly
away from half a flux quantum, we predict an enhancement of pure-dephasing by
three orders of magnitude. Employing the Floquet eigenstates as the
computational basis, we show that high-fidelity single- and two-qubit gates can
be implemented while maintaining dynamical sweet-spot operation. We further
confirm that qubit readout can be performed by adiabatically mapping the
Floquet states back to the static qubit states, and subsequently applying
standard measurement techniques. Our work provides an intuitive tool to encode
quantum information in robust, time-dependent states, and may be extended to
alternative architectures for quantum information processing
Floquet-engineered enhancement of coherence times in a driven fluxonium qubit
We use the quasienergy structure that emerges when a fluxonium
superconducting circuit is driven periodically to encode quantum information
with dynamically induced flux-insensitive sweet spots. The framework of Floquet
theory provides an intuitive description of these high-coherence working points
located away from the half-flux symmetry point of the undriven qubit. This
approach offers flexibility in choosing the flux bias point and the energy of
the logical qubit states as shown in [\textit{Huang et al., 2020}]. We
characterize the response of the system to noise in the modulation amplitude
and DC flux bias, and experimentally demonstrate an optimal working point which
is simultaneously insensitive against fluctuations in both. We observe a
40-fold enhancement of the qubit coherence times measured with Ramsey-type
interferometry at the dynamical sweet spot compared with static operation at
the same bias point.Comment: 12 pages, 7 figure
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Experimental Realization of a Protected Superconducting Circuit Derived from the 0 - π Qubit
Encoding a qubit in logical quantum states with wave functions characterized by disjoint support and robust energies can offer simultaneous protection against relaxation and pure dephasing. One of the most promising candidates for such a fully protected superconducting qubit is the 0-Ď€ circuit [Brooks et al., Phys. Rev. A 87, 052306 (2013)]. Here we realize the proposed circuit topology in an experimentally obtainable parameter regime, where the ground-state degeneracy is lifted but the qubit is still largely noise protected. More precisely, the logical states of this qubit feature disjoint support and are exponentially protected against relaxation and exponentially (first order) protected against dephasing due to charge (flux) noise. We name the resultant device the "soft 0-Ď€ qubit."Multitone spectroscopy measurements reveal the energy-level structure of the system, which can be precisely described by a simple two-mode Hamiltonian. Using a Raman-type protocol, we exploit a higher-lying charge-insensitive energy level of the device to realize coherent population transfer and logical operations. The measured relaxation (T1 = 1.6 ms) and dephasing (TR = 9 ÎĽs, T2E = 25ÎĽs) times demonstrate that the soft 0-Ď€ circuit not only broadens the family of superconducting qubits but also constitutes an important step toward quantum computing with intrinsically protected superconducting qubits
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Experimental Realization of a Protected Superconducting Circuit Derived from the 0-Ď€ Qubit
Encoding a qubit in logical quantum states with wave functions characterized by disjoint support and robust energies can offer simultaneous protection against relaxation and pure dephasing. One of the most promising candidates for such a fully protected superconducting qubit is the 0–π circuit [Brooks et al., Phys. Rev. A 87, 052306 (2013)]. Here we realize the proposed circuit topology in an experimentally obtainable parameter regime, where the ground-state degeneracy is lifted but the qubit is still largely noise protected. More precisely, the logical states of this qubit feature disjoint support and are exponentially protected against relaxation and exponentially (first order) protected against dephasing due to charge (flux) noise. We name the resultant device the “soft 0–π qubit.” Multitone spectroscopy measurements reveal the energy-level structure of the system, which can be precisely described by a simple two-mode Hamiltonian. Using a Raman-type protocol, we exploit a higher-lying charge-insensitive energy level of the device to realize coherent population transfer and logical operations. The measured relaxation (T1 = 1.6 ms) and dephasing (TR = 9 μs, T2E = 25 μs) times demonstrate that the soft 0–π circuit not only broadens the family of superconducting qubits but also constitutes an important step toward quantum computing with intrinsically protected superconducting qubits