Precise Control Of Superconducting Qubits

Quantum computation is a computational process based on the principle of quantum mechanics,which has unparalleled advantages in dealing with certain computational tasks such as solving the prime factors of composite numbers,searching a record from a large database,and simulating complex behaviors of quantum many-body systems.Quantum bits(qubits)are the core elements for information storage and processing in a quantum computer.There are many physical systems that can be used to build qubits.Superconducting qubits based on Josephson junctions have become one of the most promising candidates due to advantages in scalability,fast reading,and precise manipulation.Here we introduce the fundamental concepts of qubits,and then discuss the cryogenic platform and the measurement system for superconducting qubits in detail,with focuses on the dispersive readout and gate control of superconducting qubits.Finally,we introduce our experimental observation of non-adiabatic geometric phase in a superconducting quantum circuit.For superconducting qubits,the energy quantization and noise isolation requirements are satisfied by placing the qubit devices at very low temperatures inside a dilution refrigerator,which are connected to external circuitry via microwave cables.Auxiliary microwave modules such as filters,attenuators,amplifiers,and bias tees are used to improve the signal-to-noise ratio of the measurement system.For example,to reduce the impact of quasiparticles generated by infrared light,we have designed infrared filters.With the improved measurement system,we are able to perform an experiment of observing geometric phase in a superconducting circuit where the resonator and the qubit energy levels are dispersively coupled.We have further used the acquired geometric phase to produce the ?-phase gate with a process fidelity of 0,851 ±0.001 obtained by quantum process tomography.