Our research aims to observe and harness novel quantum mechanical effects (quantum error correction and stabilization of quantums states by feedback, for instance) through the design, fabrication, and microwave measurement of the following superconducting electrical circuit devices:

3D Transmon Qubit

This device consists of a small Josephson junction connected to a microwave antenna in the middle of a 3D cavity resonator. The 3D Transmon is an artificial atom behaving as a slightly anharmonic oscillator. Its long coherence time and simple fabrication makes it a popular superconducting qubit.


Fluxonium Qubit

This other superconducting artificial atom used in the group has a richer level structure than the transmon, but contains of order 100 Josephson junctions. It relies on an array of large Josephson junctions behaving as a superinductance, i.e. superconducting inductance whose impedance is larger than the resistance quantum. The superinductance shunts a small junction, preventing the deleterious effect of charge offsets, yet allowing quantum phase fluctuations to express themselves. The relaxation time of the fluxonium is even larger than that of the transmon due to the particular nature of its energy eigenfunctions.

Josephson Parametric Converter (JPC)

This device is based on the Josephson Ring Modulator which is a loop of four Josephson junctions threaded by an external flux. The four nodes between junctions are connected to four quarter wave transmission lines. The JPC is used in our group as a quantum limited phase-preserving amplifier, i.e. an amplifier working essentially as an op-amp for microwave signals. We use it as a pre-amplifier in the readout chain of superconducting qubits.

Josephson Bifurcation Amplifier (JBA)

This device is based on a DC SQUID ring consisting of two Josephson junctions in parallel threaded by an external flux. The junctions are shunted by an external capacitance determining the resonant frequency of the device. The JBA is used in our group as a quantum limited phase-sensitive amplifier, i.e. an amplifier that increases one quadrature of the signal at the expense of the other quadrature. We use it as an eraser of quantum information for preparing particular quantum states.