17,608 research outputs found
Complexity, parallel computation and statistical physics
The intuition that a long history is required for the emergence of complexity
in natural systems is formalized using the notion of depth. The depth of a
system is defined in terms of the number of parallel computational steps needed
to simulate it. Depth provides an objective, irreducible measure of history
applicable to systems of the kind studied in statistical physics. It is argued
that physical complexity cannot occur in the absence of substantial depth and
that depth is a useful proxy for physical complexity. The ideas are illustrated
for a variety of systems in statistical physics.Comment: 21 pages, 7 figure
Modeling and Energy Optimization of LDPC Decoder Circuits with Timing Violations
This paper proposes a "quasi-synchronous" design approach for signal
processing circuits, in which timing violations are permitted, but without the
need for a hardware compensation mechanism. The case of a low-density
parity-check (LDPC) decoder is studied, and a method for accurately modeling
the effect of timing violations at a high level of abstraction is presented.
The error-correction performance of code ensembles is then evaluated using
density evolution while taking into account the effect of timing faults.
Following this, several quasi-synchronous LDPC decoder circuits based on the
offset min-sum algorithm are optimized, providing a 23%-40% reduction in energy
consumption or energy-delay product, while achieving the same performance and
occupying the same area as conventional synchronous circuits.Comment: To appear in IEEE Transactions on Communication
Irreversibility and Entanglement Spectrum Statistics in Quantum Circuits
We show that in a quantum system evolving unitarily under a stochastic
quantum circuit the notions of irreversibility, universality of computation,
and entanglement are closely related. As the state evolves from an initial
product state, it gets asymptotically maximally entangled. We define
irreversibility as the failure of searching for a disentangling circuit using a
Metropolis-like algorithm. We show that irreversibility corresponds to
Wigner-Dyson statistics in the level spacing of the entanglement eigenvalues,
and that this is obtained from a quantum circuit made from a set of universal
gates for quantum computation. If, on the other hand, the system is evolved
with a non-universal set of gates, the statistics of the entanglement level
spacing deviates from Wigner-Dyson and the disentangling algorithm succeeds.
These results open a new way to characterize irreversibility in quantum
systems.Comment: 15 pages, 4 figure
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