# Physics Colloquium Series, Spring 2016

## Apr 7 , Thursday: 4:15 p.m. / Rockefeller 301

HongWen Jiang , UCLA

#### Can Charge Qubits Compete with Spin Qubits for Quantum Information Processing?

Semiconductor quantum dots (QDs) are a leading approach for the implementation of solid-state based qubits. In principle, either charge or spin can be used to encode a qubit. However, in the last ten years or so, a disproportionally large quantity of research has been devoted to spin qubits, mainly because of the relatively long single-qubit dephasing times for spin qubits. In this talk I present a sequence of experimental results on QD based charge qubits, demonstrating both one-qubit [1] and two-qubit [2] quantum logic operations. The finding of this research appears to go against the conventional wisdom that charge qubits are inferior in comparison to spin qubits for semiconducting materials. We found that, at the current stage, trading a shorter dephasing time for a faster qubit operation time, charge qubits can perform equivalently well in the two-qubit level. We argue that, with a better control of pulse shape and a better design of the QD dispersion relations [3], charge qubits may become a force to contend with in the scalable quantum computation arena.

[1] Gang Cao et al., "Ultrafast Universal Quantum Control of a Quantum Dot Charge Qubit Using Landau-Zener-StÃ¼ckelberg Interference", Nature Communications, 4, 1401 (2013).

[2] Hai-Ou Li et al., "Conditional Rotation of Two Strongly Coupled Semiconductor Charge Qubits", Nature Communications 15,03633 (2015).

[3] Gang Cao, et al., "Tunable Hybrid Qubit in a GaAs Double Quantum Dot ", Phys. Rev. Lett., 116, 086801 (2016).

[1] Gang Cao et al., "Ultrafast Universal Quantum Control of a Quantum Dot Charge Qubit Using Landau-Zener-StÃ¼ckelberg Interference", Nature Communications, 4, 1401 (2013).

[2] Hai-Ou Li et al., "Conditional Rotation of Two Strongly Coupled Semiconductor Charge Qubits", Nature Communications 15,03633 (2015).

[3] Gang Cao, et al., "Tunable Hybrid Qubit in a GaAs Double Quantum Dot ", Phys. Rev. Lett., 116, 086801 (2016).

Host: Arnold Dahm