Implementing a strand of a scalable fault-tolerant quantum computing fabric

Abstract

With favourable error thresholds and requiring only nearest-neighbour interactions on a lattice, the surface code is an error-correcting code that has garnered considerable attention. At the heart of this code is the ability to perform a low-weight parity measurement of local code qubits. Here we demonstrate high-fidelity parity detection of two code qubits via measurement of a third syndrome qubit. With high-fidelity gates, we generate entanglement distributed across three superconducting qubits in a lattice where each code qubit is coupled to two bus resonators. Via high-fidelity measurement of the syndrome qubit, we deterministically entangle the code qubits in either an even or odd parity Bell state, conditioned on the syndrome qubit state. Finally, to fully characterize this parity readout, we develop a measurement tomography protocol. The lattice presented naturally extends to larger networks of qubits, outlining a path towards fault-tolerant quantum computing.

Interacting two-level defects as sources of fluctuating high-frequency noise in superconducting circuits

“…Superconducting qubits 1 are well on the way towards achieving the prerequisites for fault-tolerant quantum computation schemes [2][3][4] . With the advent of highly coherent superconducting circuits for quantum applications, previously neglected sources of environmental noise become important.…”

Demonstration of Weight-Four Parity Measurements in the Surface Code Architecture

“…Typically QEC protocols function through encoding of physical qubit information onto larger subspaces, which are subsequently protected against particular quantum errors [1, 2]. Amongst the many proposed QEC codes, the topological surface code [3,4] has gathered a large amount of interest by experimental implementations [5,6] due to its use of short-range nearest-neighbor interactions between physical qubits and its relatively high error thresholds.Building up a physical quantum network with the complete functionality of the surface code brings along a number of experimental challenges, some of which have yet to be explored. However, in the particular case of superconducting qubits, recent advances in coherence times [7][8][9] and in the understanding of environmental constraints [10,11] have triggered important experimental demonstrations on increasingly larger systems, including correction of bit-flip errors on linear qubit arrays [6,12], the detection of arbitrary quantum errors [13], and state preservation via encoding in cavity coherent states [14].…”

Measurement and control of quasiparticle dynamics in a superconducting qubit

“…S uperconducting quantum circuits have made rapid progress 1 in realizing increasingly sophisticated quantum states 2,3 and operations 4,5 with high fidelity. Excitations of the superconductor, or quasiparticles (QPs), can limit their performance by causing relaxation and decoherence, with the rate approximately proportional to the QP density 6 .…”