We expect that many-core microprocessors will push performance per chip from the 10 gigaflop to the 10 teraflop range in the coming decade. To support this increased performance, memory and inter-core bandwidths will also have to scale by orders of magnitude. Pin limitations, the energy cost of electrical signaling, and the non-scalability of chip-length global wires are significant bandwidth impediments. Recent developments in silicon nanophotonic technology have the potential to meet these off-and on-stack bandwidth requirements at acceptable power levels.Corona is a 3D many-core architecture that uses nanophotonic communication for both inter-core communication and off-stack communication to memory or I/O devices. Its peak floating-point performance is 10 teraflops. Dense wavelength division multiplexed optically connected memory modules provide 10 terabyte per second memory bandwidth. A photonic crossbar fully interconnects its 256 low-power multithreaded cores at 20 terabyte per second bandwidth. We have simulated a 1024 thread Corona system running synthetic benchmarks and scaled versions of the SPLASH-2 benchmark suite. We believe that in comparison with an electrically-connected many-core alternative that uses the same on-stack interconnect power, Corona can provide 2 to 6 times more performance on many memoryintensive workloads, while simultaneously reducing power.

No abstract

We demonstrate a simple, robust, and ultrabright parametric down-conversion source of polarization-entangled photons based on a polarization Sagnac interferometer. Bidirectional pumping in type-II phase-matched periodically poled KTiOPO4 yields a measured flux of 5 000 polarization-entangled pairs/s per mW of pump power in a 1-nm bandwidth at 96.8% quantuminterference visibility. The common-path arrangement of the Sagnac interferometer eliminates the need for phase stabilization for the biphoton output state.PACS numbers: 42.65. Lm,03.65.Ud,03.67.Mn,42.50.Dv Polarization-entangled photons are essential quantum resources for many applications in quantum information processing, including quantum cryptography [1], teleportation [2], and linear optics quantum computing [3]. The standard technique for efficiently producing polarization entanglement is by means of spontaneous parametric down-conversion (SPDC) in a χ (2) nonlinear crystal such as beta barium borate (BBO) or periodically poled KTiOPO 4 (PPKTP). In SPDC a pump photon is converted into two subharmonic photons, and the SPDC outputs can be arranged in various configurations to yield polarization entanglement between the photon pair. For most practical applications, it is desirable to have a high flux of entangled photon pairs for a given spectral bandwidth, together with a high degree of entanglement. One can quantify the performance of a down-conversion source in terms of its spectral brightness, namely the detected pairs/s/mW of pump power per nm of optical bandwidth, and its quantum-interference visibility.A common approach uses a thin BBO crystal under type-II phase matching to generate non-collinearly propagating photon pairs that are polarization entangled [4]. This simple arrangement requires a small aperture to restrict the field of view in order to obtain a high degree of entanglement, and consequently the flux is generally low. A slightly different approach using a long PPKTP crystal with collinearly propagating outputs yields a higher spectral brightness of 300 pairs/s/mW/nm after postselection with a 50-50 beam splitter [5]. The increased flux is the result of a longer crystal and more efficient pair collection with the use of collinear propagation. Yet, because of spatial-mode distinguishability in both approaches, apertures must be used and most of the output photon pairs are not collected.We have recently demonstrated a bidirectionally pumped down-converter that eliminates the constraint of spatial-mode distinguishability and obtained a detected * Electronic address: thkim@mit.edu † Now at Hewlett-Packard Laboratories, 1501 Page Mill Road, Palo Alto, CA 90304, USA.flux of ∼12 000 pairs/s/mW in a 3-nm bandwidth with a quantum-interference visibility of 90% [6]. In this bidirectional pumping geometry, we used a single PPKTP crystal to implement a configuration of two coherentlydriven SPDC sources whose outputs were combined interferometrically with a Mach-Zehnder (MZ) interferometer. The output photon pairs are polarization entangled over th...

Abstract-In this letter, we present a source of quantum-correlated photon pairs based on parametric fluorescence in a fiber Sagnac loop. The photon pairs are generated in the 1550-nm fiber-optic communication band and detected with InGaAs-InP avalanche photodiodes operating in a gated Geiger mode. A generation rate 10 3 pairs/s is observed, which is limited by the detection electronics at present. We also demonstrate the nonclassical nature of the photon correlations in the pairs. This source, given its spectral properties and robustness, is well suited for use in fiber-optic quantum communication and cryptography networks.Index Terms-Fiber four-wave mixing, parametric amplifiers, photon counting, quantum communication, quantum cryptography. EFFICIENT generation and transmission of quantum-correlated photon pairs, especially in the 1550-nm fiber-optic communication band, is of paramount importance for practical realization of the quantum communication and cryptography protocols [1]. The workhorse source employed in all implementations, thus far [2] has been based on the process of spontaneous parametric down-conversion in second-order [ ] nonlinear crystals. Such a source, however, is not compatible with optical fibers as large coupling losses occur when the pairs are launched into the fiber. This severely degrades the correlated photon-pair rate coupled into the fiber, since the rate depends quadratically on the coupling efficiency. From a practical standpoint, it would be advantageous if a photon-pair source could be developed that not only produces photons in the communication band but also can be spliced to standard telecommunication fibers with high efficiency. Over the past few years, various attempts have been made to develop more efficient photon-pair sources, but all have relied on the down-conversion process [3]- [6]. Of particular note is [4], in which the effective of periodically poled silica fibers was used. In this letter, we report the first, to the best of our knowledge, photon-pair source that is based on the Kerr nonlinearity ( ) of standard fiber. Quantum-correlated photon pairs are observed and characterized in the parametric fluorescence of four-wave mixing (FWM) in dispersion-shifted fiber (DSF).The FWM process takes place in a nonlinear-fiber Sagnac interferometer (NFSI), shown schematically in Fig. 1. Previ- ously, we have used this NFSI to generate quantum-correlated twin beams in the fiber [7]. The NFSI consists of a fused-silica 50/50 fiber coupler spliced to 300 m of DSF having zero-dispersion wavelength nm. It can be set as a reflector with proper adjustment of the intraloop FPC to yield a transmission coefficient 30 dB. When the injected pump wavelength is slightly greater than , FWM in the DSF is phase matched [8]. Two pump photons of frequency scatter into a signal photon and an idler photon of frequencies and , respectively, where . Signal-idler separations of 20 nm can be easily obtained with use of commercial DSF [7]. The pump is a mode-locked train of 3-ps-long pulses that a...

We present a theoretical and experimental comparison of spontaneous parametric down-conversion in periodically poled waveguides and bulk KTP crystals. We measured a waveguide pair generation rate of 2.9.10(6) pairs/s per mWof pump in a 1-nm band: more than 50 times higher than the bulk crystal generation rate.

Multiview three-dimensional (3D) displays can project the correct perspectives of a 3D image in many spatial directions simultaneously. They provide a 3D stereoscopic experience to many viewers at the same time with full motion parallax and do not require special glasses or eye tracking. None of the leading multiview 3D solutions is particularly well suited to mobile devices (watches, mobile phones or tablets), which require the combination of a thin, portable form factor, a high spatial resolution and a wide full-parallax view zone (for short viewing distance from potentially steep angles). Here we introduce a multi-directional diffractive backlight technology that permits the rendering of high-resolution, full-parallax 3D images in a very wide view zone (up to 180 degrees in principle) at an observation distance of up to a metre. The key to our design is a guided-wave illumination technique based on light-emitting diodes that produces wide-angle multiview images in colour from a thin planar transparent lightguide. Pixels associated with different views or colours are spatially multiplexed and can be independently addressed and modulated at video rate using an external shutter plane. To illustrate the capabilities of this technology, we use simple ink masks or a high-resolution commercial liquid-crystal display unit to demonstrate passive and active (30 frames per second) modulation of a 64-view backlight, producing 3D images with a spatial resolution of 88 pixels per inch and full-motion parallax in an unprecedented view zone of 90 degrees. We also present several transparent hand-held prototypes showing animated sequences of up to six different 200-view images at a resolution of 127 pixels per inch.

Dielectric high-contrast sub-wavelength grating (SWG) structures have received much attention in recent years, offering a new paradigm for the integration of optical systems. Their nanoscale resonant properties can result in a complex and unintuitive far-field behavior that, if carefully crafted, allows the full control of the optical phase front from a thin subwavelength planar layer. To date, experimental demonstrations of these new devices have only been realized with polarized light in a reflective mode, greatly limiting their use for practical systems. In this letter, we demonstrate a highly efficient, sub-wavelength thick, transmissive grating lens configuration using symmetrical resonant posts to achieve polarization-independent operation. Our transmissive SWG lenses are easily fabricated using lowcost scalable semiconductor process technology. To illustrate their performance, we demonstrate the generation of high-order orbital angular momentum beams and their use in an optical mode-isolator application that achieves a suppression ratio of over 25 dB.

random-bit generators (RBGs) are key components of a variety of information processing applications ranging from simulations to cryptography. In particular, cryptographic systems require "strong" RBGs that produce high-entropy bit sequences, but traditional software pseudo-RBGs have very low entropy content and therefore are relatively weak for cryptography. Hardware RBGs yield entropy from chaotic or quantum physical systems and therefore are expected to exhibit high entropy, but in current implementations their exact entropy content is unknown. Here we report a quantum random-bit generator (QRBG) that harvests entropy by measuring single-photon and entangled two-photon polarization states. We introduce and implement a quantum tomographic method to measure a lower bound on the "min-entropy" of the system, and we employ this value to distill a truly random-bit sequence. This approach is secure: even if an attacker takes control of the source of optical states, a secure random sequence can be distilled.PACS numbers: 03.67. Dd,42.40.My Random numbers are commonly used in computer simulations, lotteries, and, most importantly, cryptographic applications. Cryptographically strong random numbers need to have two properties: good statistical behavior and unpredictability. The numbers need to be distributed according to a unform distribution, and an attacker should not be able to predict the corresponding sequence of bits. Unpredictability is quantified using the entropy content of a sequence generated by a random-bit generator (RBG) [16].The entropy content can be used to grade RBG security, i.e., the ability of the generator to withstand attacks. Most applications generate long strings of bits using algorithms known as pseudo-random number generators, with seeds chosen by the user. The entropy content of the strings generated in this fashion is small and is ultimately determined by the length of the (short) seed. This deficiency makes pseudo-random numbers unsuitable for the most demanding cryptographic applications. This fact has been recognized by both the information theory community and the computer security industry [1,2]. Hardware RBGs are an alternative to pseudo-RBGs because they harvest and distill entropy from physical systems. The most recent examples of hardware RBGs stress the importance of directly measuring the entropy content of the source [3].In principle, random bits could be produced by classical physical processes that are too complicated to predict perfectly over long times, such as thermal noise. For example, Denker has used thermal noise fluctuations in a resistor as a randomness source, and relied on an estimate of the entropy of the noise process to extract a random bit * Electronic address: marco.fiorentino@hp.com sequence from digits derived from that source [3]. Further, sufficiently powerful data processing systems with appropriate models or algorithms may become able to predict chaotic or thermal processes, even if only for a short time.In quantum phenomena the outcome of a class of m...