Tunable Hybrid Qubit in a GaAs Double Quantum Dot

Abstract

We experimentally demonstrate a tunable hybrid qubit in a five-electron GaAs double quantum dot. The qubit is encoded in the (1,4) charge regime of the double dot and can be manipulated completely electrically. More importantly, dot anharmonicity leads to quasiparallel energy levels and a new anticrossing, which help preserve quantum coherence of the qubit and yield a useful working point. We have performed Larmor precession and Ramsey fringe experiments near the new working point and find that the qubit decoherence time is significantly improved over a charge qubit. This work shows a new way to encode a semiconductor qubit that is controllable and coherent.

Achieving high-fidelity single-qubit gates in a strongly driven charge qubit with 1/f charge noise

“…We have developed a new scheme for effectively harnessing strong driving to perform high-fidelity gates in quantum double-dot charge qubits, even in the presence of realistic 1/f noise. Our protocol, and our analytical formalism, are both applicable to other solid-state systems, including superconducting flux qubits [38,39] and quantum-dot singlet-triplet qubits [15,40,41], and can be extended to systems with multiple levels, including quantum-dot hybrid qubits [3,11,[42][43][44][45][46] and chargequadrupole qubits [47,48]. Phonon-induced decoherence can be also analyzed in this formalism, after first averaging the phonons over the corresponding thermal distribution [34,[49][50][51].…”

“…We note that this technique is easy to use and is applicable to many other kinds of noise that are present in condensed matter devices such as Lorentzian noise and power-law noise, and can also be generalized to multi-level systems such as quantum-dot hybrid qubits [3,11,[42][43][44][45][46].…”

Semiconductor quantum computation

“…However, this qubit design relies on the valley-orbit states in silicon and thus cannot be borrowed directly. To address this problem, Cao et al in 2016 implemented this qubit in a region with more electrons, (2, 3)-(1, 4) instead of (2, 1) and (1,2), in a GaAs DQD [96]. The increased number of electrons allows tuning the mixture of charge and spin degrees freely such that the energy levels can be encoded like in a Si/SiGe DQD.…”

Quadrupolar Exchange-Only Spin Qubit

“…As with the exchange-only qubit [9], single-qubit operations in the QUEX qubit can be driven using either dc pulses or ac modulation. Compared to the exchangeonly [9-14, 18-23, 26, 39] and the hybrid [26,[40][41][42][43][44] qubit, the QUEX qubit offers an increased protection against charge noise [43,45] due to an extended charge noise sweet spot. This arises from the addition of the fourth electron which flattens the energy bands and provides a qubit energy splitting at the sweet spot which is electrically controllable and can amount to several GHz even in the "off" configuration, thus, making it compatible with conventional superconducting resonators.…”