4 research outputs found
An Experimental Microarchitecture for a Superconducting Quantum Processor
Quantum computers promise to solve certain problems that are intractable for
classical computers, such as factoring large numbers and simulating quantum
systems. To date, research in quantum computer engineering has focused
primarily at opposite ends of the required system stack: devising high-level
programming languages and compilers to describe and optimize quantum
algorithms, and building reliable low-level quantum hardware. Relatively little
attention has been given to using the compiler output to fully control the
operations on experimental quantum processors. Bridging this gap, we propose
and build a prototype of a flexible control microarchitecture supporting
quantum-classical mixed code for a superconducting quantum processor. The
microarchitecture is based on three core elements: (i) a codeword-based event
control scheme, (ii) queue-based precise event timing control, and (iii) a
flexible multilevel instruction decoding mechanism for control. We design a set
of quantum microinstructions that allows flexible control of quantum operations
with precise timing. We demonstrate the microarchitecture and microinstruction
set by performing a standard gate-characterization experiment on a transmon
qubit.Comment: 13 pages including reference. 9 figure
Logical-qubit operations in an error-detecting surface code
We realize a suite of logical operations on a distance-two logical qubit
stabilized using repeated error detection cycles. Logical operations include
initialization into arbitrary states, measurement in the cardinal bases of the
Bloch sphere, and a universal set of single-qubit gates. For each type of
operation, we observe higher performance for fault-tolerant variants over
non-fault-tolerant variants, and quantify the difference through detailed
characterization. In particular, we demonstrate process tomography of logical
gates, using the notion of a logical Pauli transfer matrix. This integration of
high-fidelity logical operations with a scalable scheme for repeated
stabilization is a milestone on the road to quantum error correction with
higher-distance superconducting surface codes.Comment: 16 pages, 9 figures, 2 table