Quantum Information Processing with Low-Frequency Fluxonium Qubits
Abstract
Despite enabling remarkable progress in the field of superconducting quantum computing transmon qubits suer from two profound limitations: (i) dielectric loss in the shunting capacitor limits the T1 time (and consequently the coherence time T2) to about 100 seven with best materials. (ii) the anharmonicity of the qubit transition is limited to on 3 ¥ 4% (200¥ 300MHz) due to the large value of the shunt required to protect from charge noise. The latter indirectly limits 2-qubit gates by, e.g., reducing dispersive shifts, enhancing the unwanted Kerr eect, and causing state leakage under strong irradiation. We propose to explore fluxoniums to overcome both limitations: initial experiments suggest that 1 ms coherence is within reach without sacrificing gate performance. Fluxonium is obtained by inductive shunting of a small junction by a chain of about 100 larger junctions. The chain (super) inductances protects the qubit from charge noise without requiring large shunting capacitors,, thereby enabling anharmonicity in excess of 1000%. Protection against surface or other dielectric loss is achieved by lowering the qubit frequency by one order of magnitude, from traditional 5¥ 10 GHz range down to 0:5¥ 1:0 GHz, and reducing the qubit transition dipole. Consequently, the lifetime goes up by a factor of 10 or more, thus opening room for millisecond coherence. Crucially, the 2-qubit gate speed does not need to be compromised thanks to the presence of transitions to higher (non-computational) levels of fluxonium. These transitions have large frequencies and dipoles, similar to a transmon, and thus enable comparable coupling constants. Our team will experimentally and theoretically address all requirements for quantum information processing with fluxoniums: optimize device design for maximal protection from decoherence in both 2D and 3D geometries; develop high-fidelity readout and state initialization; engineer and test universal 2- qubit gates using both fast flux-tuning and fixed-frequency microwave drives. If successful, our project will endow the field of superconducting quantum computing with a highly coherent and strongly non-linear artificial atom which can be readily used in all known quantum information processing scheme, from surface code to cat-states encoding to topological qubits.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1810146
Entities
People
- Vladimir E Manucharyan
Organizations
- Army Contracting Command
- National Security Agency
- University of Maryland