Abstract
We demonstrate the suppression of photon shot noise dephasing in a superconducting qubit by eliminating its dispersive coupling to the readout cavity. This is achieved in a tunable coupling qubit, where the qubit frequency and coupling rate can be controlled independently. We observe that the coherence time approaches twice the relaxation time and becomes less sensitive to thermal photon noise when the dispersive coupling rate is tuned from several MHz to 22 kHz. This work provides a promising building block in circuit quantum electrodynamics that can hold high coherence and be integrated into larger systems.
Highlights
In circuit quantum electrodynamics,[15,16] manipulation and readout of a superconducting qubit are mediated by its coupling to a transmission line cavity
The qualitative discussion above indicates that the dephasing can be suppressed by reducing (1) the photon number fluctuation, characterized by cavity decay rate κ, (2) the thermal photon population nth, and (3) the frequency shift caused by each photon, characterized by the dispersive coupling rate χ
This is realized in a tunable coupling qubit (TCQ),[20,21] where the qubit frequency and coupling strength can be tuned independently.[22]
Summary
Superconducting quantum circuits are a strong candidate for quantum computing,[1,2,3] and a convenient platform for quantum optics[4,5,6] and quantum simulation.[7,8] Extensive efforts have been made in the last decade to isolate these quantum systems from various decay channels and noise sources in the environment, leading to an increase of several orders of magnitude in energy relaxation time T1 and phase coherence time T2.9 State-of-the-art devices have achieved T1 and T2 in the millisecond regime[10,11] and pushed gate fidelity close to the threshold for fault-tolerant quantum computing.[12]. Most work in the past has adopted the first two strategies and used high-Q (>106) 3D cavities[10,18] and careful filtering and thermal anchoring to reduce κ and nth.[14,19] Here, we focus on the third approach and demonstrate the suppression of photon shot noise dephasing when χ is tuned to near zero This is realized in a tunable coupling qubit (TCQ),[20,21] where the qubit frequency and coupling strength can be tuned independently.[22] we show that measurement of the qubit state can still be performed conveniently when χ ≪ κ
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