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Chinese Physics Letters

Arbitrary and Fast Quantum Gate with Semiconductor Double-Dot Molecules on a Chip

Wei-Ping Zou, Gang Zhang, Zheng‐Yuan Xue

Published Dec 1, 2011• 1 citation
Publisher

Abstract

We propose a scheme to achieve a kind of nontrivial two-qubit operation using controllable electrons in double-dot molecules coupled to a transmission line resonator. The implemented operation is geometrical in nature and insensitive to the state of the transmission line resonator. In particular, we are able to avoid conventional dispersive coupling so that a high speed gate operation can be achieved, which is important in view of decoherence. Meanwhile, we are able to further generalize the operation to an arbitrary phase case by dynamic decoupling with two sequences.

DOI
10.1088/0256-307x/28/12/120308

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We describe a coherent control technique for coupling electron spin states associated with semiconductor double-dot molecule to a microwave stripline resonator on a chip. We identify a novel regime of operation in which strong interaction between a molecule and a resonator can be achieved with minimal decoherence, reaching the so-called strong coupling regime of cavity QED. We describe potential applications of such a system, including low-noise coherent electrical control, fast QND measurements of spin states, and long-range spin coupling.
We propose a method for implementing a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along the z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively. The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum-controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates using a box-shaped quantum dot model and numerically solving a time-dependent Schrödinger equation, and demonstrate that the quantum gates can perform quantum computations. The operating speed of the gates is about one operation per 4 ps. The reading operation of the output of the quantum computer can be performed by detecting the polarization of the qubits.
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