A valley-spin qubit in a carbon nanotube

TL;DR

This paper demonstrates a valley-spin qubit in a carbon nanotube double quantum dot, showing electrical control and coherence measurement, highlighting its potential for hyperfine interaction-free quantum computing.

Contribution

It reports the first realization of a valley-spin qubit in a carbon nanotube, with electrical manipulation and coherence measurement, advancing nanotube-based quantum computing.

Findings

Coherent control of valley-spin states via EDSR.

Measured qubit coherence time of 65 ns.

Potential for hyperfine interaction elimination.

Abstract

Although electron spins in III-V semiconductor quantum dots have shown great promise as qubits, a major challenge is the unavoidable hyperfine decoherence in these materials. In group IV semiconductors, the dominant nuclear species are spinless, allowing for qubit coherence times that have been extended up to seconds in diamond and silicon. Carbon nanotubes are a particularly attractive host material, because the spin-orbit interaction with the valley degree of freedom allows for electrical manipulation of the qubit. In this work, we realise such a qubit in a nanotube double quantum dot. The qubit is encoded in two valley-spin states, with coherent manipulation via electrically driven spin resonance (EDSR) mediated by a bend in the nanotube. Readout is performed by measuring the current in Pauli blockade. Arbitrary qubit rotations are demonstrated, and the coherence time is measured via Hahn echo. Although the measured decoherence time is only 65 ns in our current device, this work offers the possibility of creating a qubit for which hyperfine interaction can be virtually eliminated.