49 research outputs found
Superconducting qubit to optical photon transduction
Conversion of electrical and optical signals lies at the foundation of the global internet. Such converters are used to extend the reach of long-haul fibre-optic communication systems and within data centres for high-speed optical networking of computers. Likewise, coherent microwave-to-optical conversion of single photons would enable the exchange of quantum states between remotely connected superconducting quantum processors1. Despite the prospects of quantum networking, maintaining the fragile quantum state in such a conversion process with superconducting qubits has not yet been achieved. Here we demonstrate the conversion of a microwave-frequency excitation of a transmon—a type of superconducting qubit—into an optical photon. We achieve this by using an intermediary nanomechanical resonator that converts the electrical excitation of the qubit into a single phonon by means of a piezoelectric interaction and subsequently converts the phonon to an optical photon by means of radiation pressure. We demonstrate optical photon generation from the qubit by recording quantum Rabi oscillations of the qubit through single-photon detection of the emitted light over an optical fibre. With proposed improvements in the device and external measurement set-up, such quantum transducers might be used to realize new hybrid quantum networks and, ultimately, distributed quantum computers
Superconducting metamaterials for waveguide quantum electrodynamics
The embedding of tunable quantum emitters in a photonic bandgap structure
enables the control of dissipative and dispersive interactions between emitters
and their photonic bath. Operation in the transmission band, outside the gap,
allows for studying waveguide quantum electrodynamics in the slow-light regime.
Alternatively, tuning the emitter into the bandgap results in finite range
emitter-emitter interactions via bound photonic states. Here we couple a
transmon qubit to a superconducting metamaterial with a deep sub-wavelength
lattice constant (). The metamaterial is formed by periodically
loading a transmission line with compact, low loss, low disorder lumped element
microwave resonators. We probe the coherent and dissipative dynamics of the
system by measuring the Lamb shift and the change in the lifetime of the
transmon qubit. Tuning the qubit frequency in the vicinity of a band-edge with
a group index of , we observe an anomalous Lamb shift of 10 MHz
accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we
demonstrate selective enhancement and inhibition of spontaneous emission of
different transmon transitions, which provide simultaneous access to long-lived
metastable qubit states and states strongly coupled to propagating waveguide
modes.Comment: 13 pages, 7 figure
First principles study of the T-center in Silicon
The T-center in silicon is a well-known carbon-based color center that has
been recently considered for quantum technology applications. Using first
principles computations, we show that the excited state is formed by a
defect-bound exciton made of a localized defect state occupied by an electron
to which a hole is bound. The localized state is of strong carbon \textit{p}
character and reminiscent of the localization of the unpaired electron in the
ethyl radical molecule. The radiative lifetime for the defect-bound exciton is
calculated to be on the order of s, much longer than other quantum defects
such as the NV center in diamond and in agreement with experiments. The longer
lifetime is associated with the small transition dipole moment as a result of
the very different nature of the localized and delocalized states forming the
defect-bound exciton. Finally, we use first principles calculations to assess
the stability of the T-center. We find the T-center to be stable against
decomposition into simpler defects when keeping the stoichiometry fixed.
However, we identify that the T-center is easily prone to (de)hydrogenation and
so requires very precise annealing conditions (temperature and atmosphere) to
be efficiently formed