5 research outputs found
Two-Level System as a Quantum Sensor for Absolute Calibration of Power
A two-level quantum system can absorb or emit not more than one photon at a
time. Using this fundamental property, we demonstrate how a superconducting
quantum system strongly coupled to a transmission line can be used as a sensor
of the photon flux. We propose four methods of sensing the photon flux and
analyse them for the absolute calibration of power by measuring spectra of
scattered radiation from the two-level system. This type of sensor can be tuned
to operate in a wide frequency range, and does not disturb the propagating
waves when not in use. Using a two-level system as a power sensor enables a
range of applications in quantum technologies, here in particular applied to
calibrate the attenuation of transmission lines inside dilution refrigerators
Control of Localized Multiple Excitation Dark States in Waveguide QED
Subradiant excited states in finite chains of two-level quantum emitters
coupled to a one-dimensional reservoir are a resource for superior photon
storage and controlled photon manipulation. Typically, states storing multiple
excitations exhibit fermionic correlations and are thus characterized by an
anti-symmetric wavefunction, which makes them hard to prepare experimentally.
Here we identify a class of quasi-localized dark states with up to half of the
qubits excited, which appear for lattice constants that are an integer multiple
of the guided-mode wavelength. They allow for a high-fidelity preparation and
minimally invasive read out in state-of-the-art setups. In particular, we
suggest an experimental implementation using a coplanar wave-guide coupled to
superconducting transmon qubits on a chip. As free space and intrinsic losses
are minimal, virtually perfect dark states can be achieved even for a low
number of qubits, enabling fast preparation and manipulation with high
fidelity.Comment: 11 pages, 6 figure
Enhancement of Superconductivity by Amorphizing Molybdenum Silicide Films Using a Focused Ion Beam
We have used focused ion beam irradiation to progressively cause defects in annealed molybdenum silicide thin films. Without the treatment, the films are superconducting with critical temperature of about 1 K. We observe that both resistivity and critical temperature increase as the ion dose is increased. For resistivity, the increase is almost linear, whereas critical temperature changes abruptly at the smallest doses and then remains almost constant at 4 K. We believe that our results originate from amorphization of the polycrystalline molybdenum silicide films
Capacitive coupling of coherent quantum phase slip qubits to a resonator
We demonstrate capacitive coupling of coherent quantum phase slip (CQPS) flux qubits to a resonator patterned on a highly disordered TiN film. We are able to detect and characterise CQPS flux qubits with linewidths down to on several resonator modes, and show that, unlike inductive coupling, here the coupling strength does not depend on the qubit’s energy. Since the qubit is galvanically decoupled from the resonator, our approach provides flexibility in material, design and fabrication choices for CQPS-based devices. Our results are two-fold: we report CQPS in TiN and demonstrate, to our knowledge for the first time, capacitive coupling of a CQPS flux qubit