# Fluxoniums

## We work on a highly anharmonic electrical circuit, called Fluxonium, composed of a capacitance, an inductance and a Josephson junction in parallel. By changing the relative value of the energy scales associated to each of these components, we can tailor a large variety of circuits with extremely different properties ranging from high-fidelity qubits for quantum computation, long-lived (protected) qubits with engineered forbidden transitions, or use them as ancillary systems with large quantum fluctuations as a probe of other quantum systems.

Fluxonium is a type of superconducting qubit that can be used in information processing and as a quantum sensor. It was invented in 2009 in the group of Michel Devoret at Yale and gained recently a lot of interest for its potential for Quantum computation.
Fluxonium qubits are designed to have certain advantages over the others superconducting qubits, such as longer coherence times and potentially reduced sensitivity to certain types of noise. They consist of a superconducting loop made of a small Josephson junction and a large inductance making it natively sensitive to external magnetic flux.

### Key features and characteristics of fluxonium qubits

#### Long Coherence Times

One of the primary advantages of fluxonium qubits is that the matrix element controlling the sensitivity of the circuit to noise can be adjusted by design. This led to the demonstration of coherence times above a millisecond. This means that quantum information encoded in these qubits can be preserved for relatively extended periods without sacrificing on gate duration, which is crucial for error correction and practical quantum computing.

#### Anharmonicity

Fluxonium qubits typically exhibit a high anharmonicity, which is the energy difference between the first and second transition frequency of the circuit. High anharmonicity makes it easier to perform precise single-qubit operations and two-qubit gates, a fundamental requirement for quantum computation.

#### Noise Resilience

Fluxonium qubits can be designed to be less sensitive to certain types of noise, in particular material losses that couple electrically by operating at very low frequency (below 1 Gigahertz) as well as magnetic flux noise when operated at specific external magnetic flux bias.

Fluxoniums © CNRS / INSTITUT NÉEL

### Quantum computing and quantum information processing

Fluxonium qubits are still an active area of research in the field of quantum computing and quantum information processing. Scientists and engineers are continually working to improve their performance, reduce error rates, and integrate them into larger-scale quantum computing systems.