The core component of modern computers is the semiconductor chip (CPU) with full electronic control. Semiconductor quantum chip compatible with modern semiconductor technology is an important research direction of quantum computers.

A research group led by Academician GUO Guangcan from Key Laboratory of Quantum Information and Synergetic Innovation Center of Quantum Information & Quantum Physics of University of Science and Technology of China (USTC) of Chinese Academy of Sciences made progress in quantum computing based on solid quantum chip. Researchers realized the controlled-Not quantum logic gate in two-charge-qubit system of semiconductor quantum dot. Their study was published on Nature Communications with “Conditional rotation of two strongly coupled semiconductor charge qubits” as its title.

Ultrafast universal quantum control of a quantum-dot charge qubit was realized in 2013 (Nature Communications 4, 1401(2013)). Related experiments are performed on multiple qubits. Strong two-qubit coupling and precise pulse-timing are two key advances to realize two-qubit manipulation.

The researchers prepared a variety of strong coupling electric semiconductor quantum dot structure using standard semiconductor micro- and nano-fabrication processes. The coupling strength between the two qubits exceeds 100 microelectronics-volts. Applying precise control of high frequency pulses with picosecond level to quantum logic gate, they accomplished the goal of two-charge-qubit controlled-Not logic gate with the shortest manipulation time less than 200 picoseconds. The highest current level of the semiconductor two-qubit was realized with electron spins.

The new charge two-qubit system achieved fidelity as high as the spin counterparts. Although the coherence time of charge qubit is two orders of magnitude shorter than spin quantum qubit, the operation speed of charge qubit logic gate is more than two orders of magnitude faster. Charge qubit has advantages in all-electronic-manipulation method and compatibility to conventional semiconductor technology.

In the standard circuit model, arbitrary single-qubit rotations together with two-qubit controlled-NOT gate provide a universal set of quantum logic gates. This work is a solid foundation for the development of semiconductor quantum computing.

The work was supported by the Ministry of Science, the National Natural Science Foundation of China, Chinese Academy of Sciences and the Ministry of Education.

Figure: Schematic of two-qubit controlled NOT gate (Image by Guo's group)