7,627 research outputs found
Adaptive Transactional Memories: Performance and Energy Consumption Tradeoffs
Energy efficiency is becoming a pressing issue, especially in large data centers where it entails, at the same time, a non-negligible management cost, an enhancement of hardware fault probability, and a significant environmental footprint. In this paper, we study how Software Transactional Memories (STM) can provide benefits on both power saving and the overall applications’ execution performance. This is related to the fact that encapsulating shared-data accesses within transactions gives the freedom to the STM middleware to both ensure consistency and reduce the actual data contention, the latter having been shown to affect the overall power needed to complete the application’s execution.
We have selected a set of self-adaptive extensions to existing STM middlewares (namely, TinySTM and R-STM) to prove how self-adapting computation can capture the actual degree of parallelism and/or logical contention on shared data in a better way, enhancing even more the intrinsic benefits provided by STM. Of course, this benefit comes at a cost, which is the actual execution time required by the proposed approaches to precisely tune the execution parameters for reducing power consumption and enhancing execution performance. Nevertheless, the results hereby provided show that adaptivity is a strictly necessary requirement to reduce energy consumption in STM systems: Without it, it is not possible to reach any acceptable level of energy efficiency at all
Long-Distance Quantum Communication with Neutral Atoms
The architecture proposed by Duan, Lukin, Cirac, and Zoller (DLCZ) for
long-distance quantum communication with atomic ensembles is analyzed. Its
fidelity and throughput in entanglement distribution, entanglement swapping,
and quantum teleportation is derived within a framework that accounts for
multiple excitations in the ensembles as well as loss and asymmetries in the
channel. The DLCZ performance metrics that are obtained are compared to the
corresponding results for the trapped-atom quantum communication architecture
that has been proposed by a team from the Massachusetts Institute of Technology
and Northwestern University (MIT/NU). Both systems are found to be capable of
high-fidelity entanglement distribution. However, the DLCZ scheme only provides
conditional teleportation and repeater operation, whereas the MIT/NU
architecture affords full Bell-state measurements on its trapped atoms.
Moreover, it is shown that achieving unity conditional fidelity in DLCZ
teleportation and repeater operation requires ideal photon-number resolving
detectors. The maximum conditional fidelities for DLCZ teleportation and
repeater operation that can be realized with non-resolving detectors are 1/2
and 2/3, respectively.Comment: 15 pages, 10 figure
Near-term quantum-repeater experiments with nitrogen-vacancy centers: Overcoming the limitations of direct transmission
Quantum channels enable the implementation of communication tasks
inaccessible to their classical counterparts. The most famous example is the
distribution of secret key. However, in the absence of quantum repeaters, the
rate at which these tasks can be performed is dictated by the losses in the
quantum channel. In practice, channel losses have limited the reach of quantum
protocols to short distances. Quantum repeaters have the potential to
significantly increase the rates and reach beyond the limits of direct
transmission. However, no experimental implementation has overcome the direct
transmission threshold. Here, we propose three quantum repeater schemes and
assess their ability to generate secret key when implemented on a setup using
nitrogen-vacancy (NV) centers in diamond with near-term experimental
parameters. We find that one of these schemes - the so-called single-photon
scheme, requiring no quantum storage - has the ability to surpass the capacity
- the highest secret-key rate achievable with direct transmission - by a factor
of 7 for a distance of approximately 9.2 km with near-term parameters,
establishing it as a prime candidate for the first experimental realization of
a quantum repeater.Comment: 19+17 pages, 17 figures. v2: added "Discussion and future outlook"
section and expanded introduction, published versio
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