A research group led by Academician GUO Guangcan from Key Laboratory of Quantum Information and Synergetic Innovation Center of Quantum Information & Quantum Physics of USTC are making great inroads in quantum computing based on solid quantum chip. Professor GUO Guoping and Professor XIAO Ming with collaborators realized the controlled-Not quantum logic gate in two-charge-qubit system of semiconductor quantum dot. Their research was published on 17 July on the Nature Communications with “Conditional rotation of two strongly coupled semiconductor charge qubits” as its title (Nature Communications 6, 7681(2015)).
The core component of modern computers is the semiconductor chip(CPU) with full electronic control. Semiconductor quantum chip compatible with modern semiconductor technologyis an important research direction of quantum computers. The quantum chip group of Prof. GUO Guoping is always dedicated to the development of semiconductor quantum chip supported by the National Fundamental Research Program "solid-state quantum chip" project. They have successfully achieved ultrafast universal quantum control of a quantum-dot charge qubit in 2013 (Nature Communications 4,1401(2013)).
On this basis, they have recently made significant further progress on multiple qubits. Strong two-qubit coupling and precise pulse-timing are two key advances that they have made in order to realize two-qubit manupilation. They have prepared a variety of strong coupling electric semiconductor quantum dot structure, using standard semiconductor rmicro- and nano-fabrication processes. The coupling strength between the two qubits exceeds100 microelectronics-volts. They have also made great progressin precise control of high frequency pulses for quantum logic gate. Pico second-level pulse sequences were precisely made. And finally they have achieved the 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 acieved a fidelity as high as the spin counter parts: Although the coherence time of charge qubit is two orders of magnitude shorter than spin quantum qubit, the operation speed of charge qubit logic gates is more than two orders of magnitude faster. On the other hand, charge qubit has the important advantages of 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 gates, provide a universal set of quantum logic gates. This work is a solid foundation for further development of semiconductor quantum computing.
Schematic of two-qubit controlled NOT gate
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.
(LI Haiou, Quantum Information and Synergetic Innovation Center of Quantum Information & Quantum Physics)