This PDF file contains the front matter associated with SPIE Proceedings Volume 7465, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We introduce a method of using the second-order correlation of entangled photon pairs for fluorescence imaging. The method relies on the fact that one photon of the pair carries information on where the other photon has been absorbed and has produced fluorescence in a sample. Because fluorescent molecules serve as "detectors" breaking the entanglement, multiply-scattered fluorescence photons within the sample do not cause image blur. We discuss practical implementations.

We have observed a nontrivial spatial correlation and anti-correlation from a ∼200 femtosecond pulsed chaoticthermal source. The classical picture of statistical correlation of intensity fluctuations fails to give an adequate interpretation. In the view of quantum mechanics these observations are the result of two-photon interference, involving the superposition of two-photon amplitudes, nonclassical entities corresponding to different yet indistinguishable alternative ways of triggering a joint-detection event.

Since the first experiment achieving quantum ghost imaging of an opaque object, performed by the authors at the Army Research Laboratory, ghost imaging research has increased. That physics experiment resulting in the image of toy soldier created a new imaging paradigm. Prior to that all images of opaque objects were made by receiving patterns of the object from reflection and scattering of the light into a camera. In the ghost imaging experiment light patterns only came from the light source and the image was made from coincidences of those and photon counts of reflected and scattered photons received from the object. Since that original ghost imaging experiment, approximately thirteen years after ghost imaging of transmissive objects was introduced, ghost imaging is providing a new and proweful quantum tool for future improved imaging missions in the environment.

The security issue for the next generation optical network which realizes Cloud Computing System Service with data center" is urgent problem. In such a network, the encryption by physical layer which provide super security and small delay should be employed. It must provide, however, very high speed encryption because the basic link is operated at 2.5 Gbit/sec or 10 Gbit/sec. The quantum stream cipher by Yuen-2000 protocol (Y-00) is a completely new type random cipher so called Gauss-Yuen random cipher, which can break the Shannon limit for the symmetric key cipher. We develop such a cipher which has good balance of the security, speed and cost performance. In SPIE conference on quantum communication and quantum imaging V, we reported a demonstration of 2.5 Gbit/sec system for the commercial link and proposed how to improve it to 10 Gbit/sec. This paper reports a demonstration of the Y-00 cipher system which works at 10 Gbit/sec. A transmission test in a laboratory is tried to get the basic data on what parameters are important to operate in the real commercial networks. In addition, we give some theoretical results on the security. It is clarified that the necessary condition to break the Shannon limit requires indeed the quantum phenomenon, and that the full information theoretically secure system is available in the satellite link application.

This paper is concerned with the intensity modulation-based quantum stream cipher by Yuen 2000 protocol with a nonlinear pseudorandom number generator. First we show the minimum error probability of the basic model of the intensity modulation-based quantum stream cipher in cases of ciphertext-only attacks and known plaintext attack, by using the quantum signal detection theory. Second we propose the intensity modulation-based quantum stream cipher having a nonlinear pseudorandom number generator that is realized by the basis converter. We compare the error profile of the system having the nonlinear pseudorandom number generator with that of the basic model. As a result we will see that the use of the nonlinear pseudorandom number generator yields an advantage to the legitimate users.

We report the development of a fiber-based single-spatial-mode source of photon-pairs where the efficiency of extracting photon pairs is 14× higher than a previous implementation [16]. This critical improvement in efficiency enabled a spectrally bright and pure photon-pair source having a small second-order correlation function (0.03) and a raw spectral brightness of 44,700 pairs/(s nm mW). The source can be configured to generate entangled photon-pairs, characterized via optimal and minimal quantum state tomography, to have a fidelity of 97% and tangle of 92%, without correcting for accidentals.

Efficiently creating optical quantum states, both simple (e.g., pure single-photon states) and complex (e.g., polarization-entangled but spectrally unentangled photon pairs), remains an experimental challenge. We report on a novel method that allows for efficiently preparing certain classes of states: by weakly driving repeated downconversion in a cavity, we can pseudo-deterministically add photons to a state, preparing Fock states of definite photon number. We discuss expected performance and experimental limitations, including the difficulty of creating pure photons at a high rate. Additionally, we report on our progress in engineering high-rate spatio-spectrally unentangled downconversion, a key technology for optical quantum information processing, and propose a novel 4-photon experimental scheme to test the intrinsic indistinguishability of the photons from this source.

A pair of optical pulses traveling through two dispersive media will become broadened and, as a result, the degree of coincidence between the optical pulses will be reduced. For a pair of entangled photons, however, nonlocal dispersion cancellation in which the dispersion experienced by one photon cancels the dispersion experienced by the other photon is possible. In this paper, we report an experimental demonstration of nonlocal dispersion cancellation using entangled photons. The degree of two-photon coincidence is shown to increase beyond the limit attainable without entanglement. Our results have important applications in fiber-based quantum communication and quantum metrology.

We observed the second order correlation peak for nondegenerate spontaneous parametric down conversion (SPDC) of a pulsed pump at 532 nm into 810 nm and 1550 nm entangled beams. We used a Si avalanche photodiode (APD) to detect the 810 nm photons, and an InGaAs APD to detect those at 1550 nm. We defined both a visibility and signal-to-noise ratio (SNR) based on the data, which were obtained at various pump powers. In contrast to classical imaging systems, for which SNR increases monotonically with transmitted power, the SNR for the correlation peak in our setup exhibited a gradual decay as the pump power increased. We derived an empirical relation for the SNR, which was inversely proportional to the square root of pump power.

A compact scheme for high-speed frequency doubling and down-conversion on a single dual-element PPKTP waveguide is investigated. Optimal temperature is achieved and photon pair coincidence is observed at over GHz repetition rate with pulsed pump input scheme.

We present a systematic study of a correlated photon-pair source based on a periodically-poled KTiOPO₄ (PPKTP) waveguide. The waveguide was fabricated on a KTiOPO₄ crystal supporting type-II parametric down-conversion. In addition, periodic poling was applied along the waveguide to quasi-phase-match the type-0 down-conversion process. The design pump wavelength is 532 nm, and the wavelengths of the down-converted, correlated photons are around 900 nm and 1300 nm. We examine the two-photon correlation spectra and singlephoton spectra at a variety of temperature and power settings for both type-0 and type II down-conversion processes. Our study shows that the waveguide source has a number of advantages compared to its bulk-crystal counterpart, including higher spectral brightness, narrower emission bandwidth and single spatial-mode output. With greatly simplified engineering, this compact, highly efficient, low photon-loss, and cost-effective waveguide source of correlated photon pairs is promising for future chip-scale quantum information processing applications.

Chirped-pulse interferometry is a new interferometric technique encapsulating the advantages of the quantum Hong-Ou-Mandel interferometer without the drawbacks of using entangled photons. Both interferometers can exhibit even-order dispersion cancellation which allows high resolution optical delay measurements even in thick optical samples. In the present work, we show that finite frequency correlations in chirped-pulse interferometry and Hong-Ou-Mandel interferometry limit the degree of dispersion cancellation. Our results are important considerations in designing practical devices based on these technologies.

We present a novel quantum communication protocol for "Private Data Sampling", where a player (Bob) obtains a random sample of limited size of a classical database, while the database owner (Alice) remains oblivious as to which bits were accessed. The protocol is efficient in the sense that the communication complexity per query scales at most linearly with the size of the database. It does not violate Lo's "no-go" theorem for one-sided twoparty secure computation, since a given joint input by Alice and Bob can result in randomly different protocol outcomes. After outlining the main security features of the protocol, we present our first experimental results.

We will describe a new factorization algorithm based on the reproduction of continuous exponential sums, using the interference pattern produced by polychromatic light interacting with an interferometer with variable optical paths. We will describe two possible interferometers: a generalized symmetric Michelson interferometer and a liquid crystal grating. Such an algorithm allows, for the first time, to find all the factors of a number N in a single run without precalculating the ratio N/l, where l are all the possible trial factors. It also allows to solve the problem of ghost factors and to factorize different numbers using the same output interference pattern.

We developed low-noise up-conversion single photon detectors for 1310 nm based on a periodically-poled LiNbO₃ (PPLN) waveguide. The low-noise feature is achieved by using a pulsed optical pump at a wavelength longer than the signal wavelength. The detectors were used in a quantum key distribution (QKD) systems based on polarization encoding, measurement for entangled photon pairs and spectrum measurement at single photon levels. In this paper, the overall detection efficiency and noise level of the detectors are characterized and the polarization and wavelength sensitivity of the detection efficiency is analyzed. The applications of this detector in quantum information systems are also described.

We present a new concept for birefringence compensation in Sagnac single mode fiber (SMF) interferometer, which has opened the door to secure multiuser quantum communications. The concept has been tested in both quantum key distribution (QKD) and secret sharing applications at total fiber loop lengths up to 150 km. Now, we present a Jones matrix based model of the concept as well as the visibility measurements confirming its practical validity. Sagnac based circular SMF network architecture is an attractive solution for both commercial telecom Intranets and backbone networks as well as for secure quantum information channels exploring QKD and secret sharing applications. Due to the difference in birefringence between the clockwise and counterclockwise transmission directions, Sagnac has not been so much explored by the quantum information community as other network architectures, especially the "plug & play". Our SMF Sagnac birefringence compensation uses polarization maintaining, horizontally aligned components only, except for the SMF fiber link. It converts the arbitrary elliptically polarized clockwise and counterclockwise light signals, transmitted over the SMF fiber, into the horizontal polarization. Thus, both the sent and received light signals have the same horizontal polarization. In order to avoid unnecessary power losses in the birefringence compensator, we have included a simple proportional-integral-derivative controller into our setup. The compensator provides a perfect birefringence compensation for the destructive interference, which leads to a high system visibility. The presented SMF Sagnac birefringence compensation could also be use in Sagnac metrology, for instance in very low power level sensing, requiring high measurement accuracy.

The errors in linear optics controlled not (C-NOT) gates are analyzed considering the polarization-dependent phase sifts, in addition to the incorrectness of the beam splitting ratios. It is shown that the phase sifts at the optical components is as crucial as other error sources discussed in the previous studies. Such a phase shift unintentionally changes the linearly-polarized photons into a elliptically polarized ones. The operators for a beam splitting device and the process matrix of the C-NOT operation including such errors are also given.