Superconducting circuits constitue a promising platform for physically realizing a quantum computer. One of the most fundamental operations of a quantum computer is to measure the state of its quantum bits (qubits). The measurement process should be as fast as possible, in order to minimize errors in the computation caused by noise. Conventionally, the state of a qubit in a superconducting circuit is determined by coupling the qubit to a readout resonator and measuring how the state of the resonator changes when a readout pulse is applied to it. Recently, a method was proposed that makes it possible to read out the state of a qubit faster by applying pulses to both the resonator and the qubit simultaneously. In this thesis, we study whether this so-called multichannel technique could be used to unconditionally drive the readout resonator back to its initial state after the readout has been finished. Using numerical simulations, we find that compared to just waiting passively, the time it takes to initialize the resonator can be reduced by up to 86%. We also implement a part of the initialization protocol experimentally and find the results encouraging for the future implementation of the full protocol.
A key challenge in quantum computing is speeding up measurement and initialization. Here, we experimentally demonstrate a dispersive measurement method for superconducting qubits that simultaneously measures the qubit and returns the readout resonator to its initial state. The approach is based on universal analytical pulses and requires knowledge of the qubit and resonator parameters, but needs no direct optimization of the pulse shape, even when accounting for the nonlinearity of the system. Moreover, the method generalizes to measuring an arbitrary number of modes and states. For the qubit readout, we can drive the resonator to
∼102 photons and back to
∼10−3 photons in less than
3κ−1, while still achieving a
T1-limited assignment error below 1\%. We also present universal pulse shapes and experimental results for qutrit readout.
A key challenge in quantum computing is speeding up measurement and initialization. Here, we experimentally demonstrate a dispersive measurement method for superconducting qubits that simultaneously measures the qubit and returns the readout resonator to its initial state. The approach is based on universal analytical pulses and requires knowledge of the qubit and resonator parameters, but needs no direct optimization of the pulse shape, even when accounting for the nonlinearity of the system. Moreover, the method generalizes to measuring an arbitrary number of modes and states. For the qubit readout, we can drive the resonator to
∼102 photons and back to
∼10−3 photons in less than
3κ−1, while still achieving a
T1-limited assignment error below 1\%. We also present universal pulse shapes and experimental results for qutrit readout.