We report ellipsometric measurements made on semiconductor samples using photon-correlated beams produced by the process of spontaneous parametric down-conversion. Such a source yields higher accuracy than its quantum-limited conventional counterpart. We also show that our approach has the added advantage of not requiring an external reference sample for calibration. I. BACKGROUNDSince all optical measurements are limited by quantum noise, which dominates at low light levels, there has been a strong interest in developing nonclassical optical sources with sub-Poisson photon statistics that offer sub-shot-noise accuracy. One implementation that has been considered for metrology applications is based on the use of two optical beams, each with Poisson-distributed photons, but also with a fully correlated joint photon counting distribution. Such correlated-photon beams have been generated, for example, by spontaneous parametric down-conversion (SPDC) in a nonlinear optical crystal, and used for applications including quantum cryptography [1], teleportation [2], and metrology [3,4]. If one of the beams is reflected from, or transmitted through, a sample, then measurement of the photon coincidence rate, together with the mean photon counts in each beam, yield estimates of the sample reflectance/transmittance with accuracy greater than the conventional measurement using a single beam [5][6][7][8][9]. In this paper, we consider the use of photon-correlated beams in ellipsometry.Ellipsometry [10-15] is a technique in which the polarization of light is used to determine the optical properties of a material (sample) and infer information such as the thickness of a thin film. The sample is characterized by two parameters = arctan͉ r 2 / r 1 ͉ and ⌬ = arg͑r 2 / r 1 ͒ where r 1 and r 2 are the sample's eigenpolarization complex reflection coefficients [11]. In a conventional ellipsometer, these parameters are extracted by manipulation of the polarization state of the incident or the reflected/transmitted light and measurement of the optical intensities or the photon counting rates. Clearly, such measurements are limited by shot noise, particularly at low light intensities or when using ellipsometers employing a nulling technique. The use of photon-correlated beams in ellipsometry has been previously reported and referred to as "quantum ellipsometry" [16,17]. It was shown that this technique alleviates the need for calibration using an external reference sample.In this paper, we report experimental quantum ellipsometric measurements made on standard optical samples. We also estimate the accuracy advantage attained by the use of quantum relative to conventional ellipsometry. Section II of the paper reviews the theory of correlated-photon ellipsometry, a form of quantum ellipsometry. Although correlated-photon pairs may be generated by a variety of means, correlatedphoton ellipsometry in this paper refers to the use of photon pairs generated by SPDC. In Sec. III we present experimental results obtained from two semiconductor sa...

Register files are becoming one of the critical components of current out-of-order

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Thread-Level Speculation (TLS) provides architectural support to aggressively run hard-to-analyze code in parallel. As speculative tasks run concurrently, they generate unsafe or speculative memory state that needs to be separately buffered and managed in the presence of distributed caches and buffers. Such a state may contain multiple versions of the same variable. In this paper, we introduce a novel taxonomy of approaches to buffer and manage multiversion speculative memory state in multiprocessors. We also present a detailed complexity-benefit tradeoff analysis of the different approaches. Finally, we use numerical applications to evaluate the performance of the approaches under a single architectural framework. Our key insights are that support for buffering the state of multiple speculative tasks and versions per processor is more complexity-effective than support Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or direct commercial advantage and that copies show this notice on the first page or initial screen of a display along with the full citation. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, to redistribute to lists, or to use any component of this work in other works requires prior specific permission and/or a fee. Permissions may be requested from Publications Dept., ACM, Inc., 1515 Broadway, New York, NY 10036 USA, fax: +1 ( for lazily merging the state of tasks with main memory. Moreover, both supports can be gainfully combined and, in large machines, their effect is nearly fully additive. Finally, the more complex support for storing future state in the main memory can boost performance when buffers are under pressure, but hurts performance when squashes are frequent.

Optimization of the replacement policy used for Shared Last-Level Cache (SLLC) management in a Chip-MultiProcessor (CMP) is critical for avoiding off-chip accesses. Temporal locality, while being exploited by first levels of private cache memories, is only slightly exhibited by the stream of references arriving at the SLLC. Thus, traditional replacement algorithms based on recency are bad choices for governing SLLC replacement. Recent proposals involve SLLC replacement policies that attempt to exploit reuse either by segmenting the replacement list or improving the rereference interval prediction. On the other hand, inclusive SLLCs are commonplace in the CMP market, but the interaction between replacement policy and the enforcement of inclusion has barely been discussed. After analyzing that interaction, this article introduces two simple replacement policies exploiting reuse locality and targeting inclusive SLLCs: Least Recently Reused (LRR) and Not Recently Reused (NRR). NRR has the same implementation cost as NRU, and LRR only adds one bit per line to the LRU cost. After considering reuse locality and its interaction with the invalidations induced by inclusion, the proposals are evaluated by simulating multiprogrammed workloads in an 8-core system with two private cache levels and an SLLC. LRR outperforms LRU by 4.5% (performing better in 97 out of 100 mixes) and NRR outperforms NRU by 4.2% (performing better in 99 out of 100 mixes). We also show that our mechanisms outperform rereference interval prediction, a recently proposed SLLC replacement policy and that similar conclusions can be drawn by varying the associativity or the SLLC size.