A quantum computer is a new type of device that could harness the power of quantum superposition, quantum entanglement, and quantum interference to dramatically reduce computation time for challenging problems. So far, quantum computational operations have only been realized in systems with a small number of quantum bits (qubits). The difficulty is that qubits are very sensitive to noise in their environment, which causes them to lose their quantum properties before there is enough time to perform any calculations. One way to improve the qubits is to develop new designs, using new materials and more refined fabrication techniques. A complimentary approach is to actively counteract the negative influence of the noise by applying a sequence of control pulses to the qubits, which decouples them from the noisy environment. This project will develop and implement such dynamical decoupling techniques for systems with coupled qubits, with the goal of further improving qubit performance and reducing error rates in multi-qubit systems.
Any realistic quantum computer will need to implement error correction algorithms, so that residual errors can be handled as they occur. There exist several proposals for implementing quantum error correction, but common to protocols is that they put stringent requirements on the allowed error rate for performing single and multi-qubit gate operations. Even though contemporary qubit designs are close to threshold for certain protocols, it is important to realize that most quantum error correction protocols assume that the errors of individual qubits are uncorrelated, which is an oversimplification for most physical qubit systems. This project will focus on quantifying correlated noise in multi-qubit systems, which will be key for the development of more efficient quantum error correction protocols. In addition, this team will develop novel qubit control sequences for dynamically improving both qubit relaxation and dephasing times by reducing the number of quasiparticles close to the device.