2,671 research outputs found
Magic-State Functional Units: Mapping and Scheduling Multi-Level Distillation Circuits for Fault-Tolerant Quantum Architectures
Quantum computers have recently made great strides and are on a long-term
path towards useful fault-tolerant computation. A dominant overhead in
fault-tolerant quantum computation is the production of high-fidelity encoded
qubits, called magic states, which enable reliable error-corrected computation.
We present the first detailed designs of hardware functional units that
implement space-time optimized magic-state factories for surface code
error-corrected machines. Interactions among distant qubits require surface
code braids (physical pathways on chip) which must be routed. Magic-state
factories are circuits comprised of a complex set of braids that is more
difficult to route than quantum circuits considered in previous work [1]. This
paper explores the impact of scheduling techniques, such as gate reordering and
qubit renaming, and we propose two novel mapping techniques: braid repulsion
and dipole moment braid rotation. We combine these techniques with graph
partitioning and community detection algorithms, and further introduce a
stitching algorithm for mapping subgraphs onto a physical machine. Our results
show a factor of 5.64 reduction in space-time volume compared to the best-known
previous designs for magic-state factories.Comment: 13 pages, 10 figure
Destroying a topological quantum bit by condensing Ising vortices
The imminent realization of topologically-protected qubits in fabricated
systems will provide not only an elementary implementation of fault-tolerant
quantum computing architecture, but also an experimental vehicle for the
general study of topological order. The simplest topological qubit harbors what
is known as a Z liquid phase, which encodes information via a degeneracy
depending on the system's topology. Elementary excitations of the phase are
fractionally charged objects called {\it spinons}, or Ising flux vortices
called {\it visons}. At zero temperature a Z liquid is stable under
deformations of the Hamiltonian until spinon or vison condensation induces a
quantum phase transition destroying the topological order. In this paper, we
use quantum Monte Carlo to study a vison-induced transition from a Z liquid
to a valence-bond solid in a quantum dimer model on the kagome lattice. Our
results indicate that this critical point is controlled by a new universality
class beyond the standard Landau paradigm.Comment: 5 pages, 4 figures. Published versio
Recursive quantum repeater networks
Internet-scale quantum repeater networks will be heterogeneous in physical
technology, repeater functionality, and management. The classical control
necessary to use the network will therefore face similar issues as Internet
data transmission. Many scalability and management problems that arose during
the development of the Internet might have been solved in a more uniform
fashion, improving flexibility and reducing redundant engineering effort.
Quantum repeater network development is currently at the stage where we risk
similar duplication when separate systems are combined. We propose a unifying
framework that can be used with all existing repeater designs. We introduce the
notion of a Quantum Recursive Network Architecture, developed from the emerging
classical concept of 'recursive networks', extending recursive mechanisms from
a focus on data forwarding to a more general distributed computing request
framework. Recursion abstracts independent transit networks as single relay
nodes, unifies software layering, and virtualizes the addresses of resources to
improve information hiding and resource management. Our architecture is useful
for building arbitrary distributed states, including fundamental distributed
states such as Bell pairs and GHZ, W, and cluster states.Comment: 14 page
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