52 research outputs found
Quantum Divide and Compute: Hardware Demonstrations and Noisy Simulations
Noisy, intermediate-scale quantum computers come with intrinsic limitations
in terms of the number of qubits (circuit "width") and decoherence time
(circuit "depth") they can have. Here, for the first time, we demonstrate a
recently introduced method that breaks a circuit into smaller subcircuits or
fragments, and thus makes it possible to run circuits that are either too wide
or too deep for a given quantum processor. We investigate the behavior of the
method on one of IBM's 20-qubit superconducting quantum processors with various
numbers of qubits and fragments. We build noise models that capture
decoherence, readout error, and gate imperfections for this particular
processor. We then carry out noisy simulations of the method in order to
account for the observed experimental results. We find an agreement within 20%
between the experimental and the simulated success probabilities, and we
observe that recombining noisy fragments yields overall results that can
outperform the results without fragmentation.Comment: Accepted in ISVLSI 202
Comparing the Overhead of Topological and Concatenated Quantum Error Correction
This work compares the overhead of quantum error correction with concatenated
and topological quantum error-correcting codes. To perform a numerical
analysis, we use the Quantum Resource Estimator Toolbox (QuRE) that we recently
developed. We use QuRE to estimate the number of qubits, quantum gates, and
amount of time needed to factor a 1024-bit number on several candidate quantum
technologies that differ in their clock speed and reliability. We make several
interesting observations. First, topological quantum error correction requires
fewer resources when physical gate error rates are high, white concatenated
codes have smaller overhead for physical gate error rates below approximately
10E-7. Consequently, we show that different error-correcting codes should be
chosen for two of the studied physical quantum technologies - ion traps and
superconducting qubits. Second, we observe that the composition of the
elementary gate types occurring in a typical logical circuit, a fault-tolerant
circuit protected by the surface code, and a fault-tolerant circuit protected
by a concatenated code all differ. This also suggests that choosing the most
appropriate error correction technique depends on the ability of the future
technology to perform specific gates efficiently
Implementation of Provably Stable MaxNet
MaxNet TCP is a congestion control protocol that uses explicit multi-bit signalling from routers to achieve desirable properties such as high throughput and low latency. In this paper we present an implementation of an extended version of MaxNet. Our contributions are threefold. First, we extend the original algorithm to give both provable stability and rate fairness. Second, we introduce the MaxStart algorithm which allows new MaxNet connections to reach their fair rates quickly. Third, we provide a Linux kernel implementation of the protocol. With no overhead but 24-bit price signals, our implementation scales from 32 bit/s to 1 peta-bit/s with a 0.001% rate accuracy. We confirm the theoretically predicted properties by performing a range of experiments at speeds up to 1 Gbit/sec and delays up to 180 ms on the WAN-in-Lab facility
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