12 research outputs found
Inductively shunted transmon qubit with tunable transverse and longitudinal coupling
We present the design of an inductively shunted transmon qubit with
flux-tunable coupling to an embedded harmonic mode. This circuit construction
offers the possibility to flux-choose between pure transverse and pure
longitudinal coupling, that is coupling to the or degree
of freedom of the qubit. While transverse coupling is the coupling type that is
most commonly used for superconducting qubits, the inherently different
longitudinal coupling has some remarkable advantages both for readout and for
the scalability of a circuit. Being able to choose between both kinds of
coupling in the same circuit provides the flexibility to use one for coupling
to the next qubit and one for readout, or vice versa. We provide a detailed
analysis of the system's behavior using realistic parameters, along with a
proposal for the physical implementation of a prototype device.Comment: 14 pages, 14 figure
An argon ion beam milling process for native layers enabling coherent superconducting contacts
We present an argon ion beam milling process to remove the native oxide layer
forming on aluminum thin films due to their exposure to atmosphere in between
lithographic steps. Our cleaning process is readily integrable with
conventional fabrication of Josephson junction quantum circuits. From
measurements of the internal quality factors of superconducting microwave
resonators with and without contacts, we place an upper bound on the residual
resistance of an ion beam milled contact of 50 at a frequency of 4.5 GHz. Resonators for which only of the
total foot-print was exposed to the ion beam milling, in areas of low electric
and high magnetic field, showed quality factors above in the single
photon regime, and no degradation compared to single layer samples. We believe
these results will enable the development of increasingly complex
superconducting circuits for quantum information processing.Comment: 4 pages, 4 figures, supplementary materia
Multi-photon dressing of an anharmonic superconducting many-level quantum circuit
We report on the investigation of a superconducting anharmonic multi-level
circuit that is coupled to a harmonic readout resonator. We observe
multi-photon transitions via virtual energy levels of our system up to the
fifth excited state. The back-action of these higher-order excitations on our
readout device is analyzed quantitatively and demonstrated to be in accordance
with theoretical expectation. By applying a strong microwave drive we achieve
multi-photon dressing within our anharmonic circuit which is dynamically
coupled by a weak probe tone. The emerging higher-order Rabi sidebands and
associated Autler-Townes splittings involving up to five levels of the
investigated anharmonic circuit are observed. Experimental results are in good
agreement with master equation simulations.Comment: 9 pages, 5 figure
Rabi oscillations in a superconducting nanowire circuit
We investigate the circuit quantum electrodynamics of anharmonic superconducting nanowire oscillators. The sample circuit consists of a capacitively shunted nanowire with a width of about 20 nm and a varying length up to 350 nm, capacitively coupled to an on-chip resonator. By applying microwave pulses we observe Rabi oscillations, measure coherence times and the anharmonicity of the circuit. Despite the very compact design, simple top-down fabrication and high degree of disorder in the oxidized (granular) aluminum material used, we observe lifetimes in the microsecond range
Quasiparticle dynamics in granular aluminum close to the superconductor to insulator transition
Superconducting high kinetic inductance elements constitute a valuable
resource for quantum circuit design and millimeter-wave detection. Granular
aluminum (GrAl) in the superconducting regime is a particularly interesting
material since it has already shown a kinetic inductance in the range of
nH and its deposition is compatible with conventional Al/AlOx/Al
Josephson junction fabrication. We characterize microwave resonators fabricated
from GrAl with a room temperature resistivity of cm, which is a factor of 3 below the superconductor to
insulator transition, showing a kinetic inductance fraction close to unity. The
measured internal quality factors are on the order of
in the single photon regime, and we demonstrate that non-equilibrium
quasiparticles (QP) constitute the dominant loss mechanism. We extract QP
relaxation times in the range of 1 s and we observe QP bursts every
s. The current level of coherence of GrAl resonators makes them attractive for
integration in quantum devices, while it also evidences the need to reduce the
density of non-equilibrium QPs.Comment: 5 pages, 4 figures, supplementary materia