We present a type of transmon split-junction qubit which can be tuned by Meissner screening currents flowing in the adjacent superconducting film electrodes. The best detected relaxation time $({T}_{1})$ was of the order of $50\ensuremath{\mu}\mathrm{s}$ and the dephasing time $({T}_{2})$ about $40\ensuremath{\mu}\mathrm{s}$. The achieved period of oscillation with magnetic field was much smaller than in the usual SQUID-based transmon qubits; thus a strong effective field amplification has been realized. This Meissner qubit allows a strong mixing of the current flowing in the qubit junctions and the currents generated by the Abrikosov vortices. We present a quantitative analysis of the radiation-free relaxation in qubits coupled to the Abrikosov vortices. The observation of coherent quantum oscillations provides strong evidence that the position of the vortex as well as its velocity do not have to accept exact values but can be smeared in the quantum mechanical sense. The eventual relaxation of such states contributes to an increased relaxation rate of the qubit coupled to vortices. Such relaxation is described using basic notions of the Caldeira-Leggett quantum dissipation theory.We present a type of transmon split-junction qubit which can be tuned by Meissner screening currents flowing in the adjacent superconducting film electrodes. The best detected relaxation time $({T}_{1})$ was of the order of $50\ensuremath{\mu}\mathrm{s}$ and the dephasing time $({T}_{2})$ about $40\ensuremath{\mu}\mathrm{s}$. The achieved period of oscillation with magnetic field was much smaller than in the usual SQUID-based transmon qubits; thus a strong effective field amplification has been realized. This Meissner qubit allows a strong mixing of the current flowing in the qubit junctions and the currents generated by the Abrikosov vortices. We present a quantitative analysis of the radiation-free relaxation in qubits coupled to the Abrikosov vortices. The observation of coherent quantum oscillations provides strong evidence that the position of the vortex as well as its velocity do not have to accept exact values but can be smeared in the quantum mechanical sense. The eventual relaxation of such states contributes to an increased relaxation rate of the qubit coupled to vortices. Such relaxation is described using basic notions of the Caldeira-Leggett quantum dissipation theory.

arXiv:1504.03360Physical review. B./Physical review. BOct 14, 201611 citations

Sources of decoherence in fixed frequency transmon qubits

Andreas Fuhrer, Matthias Mergenthaler, Peter R. Müeller +6 more

Bulletin of the American Physical SocietyMar 6, 20190 citations

Coherence and Decay of Higher Energy Levels of a Superconducting Transmon Qubit

Michael Peterer, Samuel James Bader, Xiaoyue Jin +7 more

We present measurements of coherence and successive decay dynamics of higher energy levels of a superconducting transmon qubit. By applying consecutive π pulses for each sequential transition frequency, we excite the qubit from the ground state up to its fourth excited level and characterize the decay and coherence of each state. We find the decay to proceed mainly sequentially, with relaxation times in excess of 20 μs for all transitions. We also provide a direct measurement of the charge dispersion of these levels by analyzing beating patterns in Ramsey fringes. The results demonstrate the feasibility of using higher levels in transmon qubits for encoding quantum information.We present measurements of coherence and successive decay dynamics of higher energy levels of a superconducting transmon qubit. By applying consecutive π pulses for each sequential transition frequency, we excite the qubit from the ground state up to its fourth excited level and characterize the decay and coherence of each state. We find the decay to proceed mainly sequentially, with relaxation times in excess of 20 μs for all transitions. We also provide a direct measurement of the charge dispersion of these levels by analyzing beating patterns in Ramsey fringes. The results demonstrate the feasibility of using higher levels in transmon qubits for encoding quantum information.

arXiv:1409.6031Physical Review LettersJan 6, 2015207 citations

We present a type of transmon split-junction qubit which can be tuned by Meissner screening currents flowing in the adjacent superconducting film electrodes. The best detected relaxation time

({T}_{1})

was of the order of $50\ensuremath{\mu}\mathrm{s}$ and the dephasing time

({T}_{2})

about $40\ensuremath{\mu}\mathrm{s}$. The achieved period of oscillation with magnetic field was much smaller than in the usual SQUID-based transmon qubits; thus a strong effective field amplification has been realized. This Meissner qubit allows a strong mixing of the current flowing in the qubit junctions and the currents generated by the Abrikosov vortices. We present a quantitative analysis of the radiation-free relaxation in qubits coupled to the Abrikosov vortices. The observation of coherent quantum oscillations provides strong evidence that the position of the vortex as well as its velocity do not have to accept exact values but can be smeared in the quantum mechanical sense. The eventual relaxation of such states contributes to an increased relaxation rate of the qubit coupled to vortices. Such relaxation is described using basic notions of the Caldeira-Leggett quantum dissipation theory.