We present a transmon qubit fabrication technique that yields systematic improvements in T
1 relaxation times. We encapsulate the surface of niobium and prevent the formation of its …

Superconducting circuits are among the most advanced quantum computing technologies;
however, their performance is limited by losses found in surface oxides and disordered …

State-of-the-art transmon qubits rely on large capacitors, which systematically improve their
coherence due to reduced surface-loss participation. However, this approach increases both …

We experimentally assess the suitability of transmon qubits with fixed frequencies and fixed
interactions for the realization of analogue quantum simulations of spin systems. We test a …

Two-level systems (TLSs) are the major source of dephasing of spin qubits in numerous
quantum computing platforms. In spite of much effort, it has been difficult to substantially …

In this study, we rigorously derived the survival probability in a time-dependent Ising chain
coupled with a bosonic system at zero temperature. We found that nonadiabatic transitions …

We investigate the pure dephasing of a Josephson qubit due to the spectral diffusion of two-
level systems that are close to resonance with the qubit. We identify the parameter regime in …

Recent experimental evidences point to two-level defects, located in the oxides and on the
interfaces of the Josephson junctions, as the major constituents of decoherence in …

Frequency instabilities are a major source of errors in quantum devices. This Letter
investigates frequency fluctuations in a surface acoustic wave (SAW) resonator, where …

Temporal fluctuations in the superconducting qubit lifetime, $ T_1 $, bring up additional
challenges in building a fault-tolerant quantum computer. While the exact mechanisms …