Efficient and spectrally bright source of polarization-entangled photons

We demonstrate an efficient fiber-coupled source of nondegenerate polarization entangled photons at 795 and 1609 nm using bidirectionally pumped parametric down-conversion in bulk periodically poled lithium niobate. The single-mode source has an inferred bandwidth of 50 GHz and a spectral brightness of 300 pairs/s/GHz/mW of pump power that is suitable for narrowband applications such as entanglement transfer from photonic to atomic qubits.Comment: 8 pages, 7 figures, submitted to Phys. Rev.

Two-photon coincident-frequency-entanglement via extended phase matching

We demonstrate a new class of frequency-entangled states generated via spontaneous parametric down-conversion under extended phase matching conditions. Biphoton entanglement with coincident signal and idler frequencies is observed over a broad bandwidth in periodically poled KTiOPO$_4$. We demonstrate high visibility in Hong-Ou-Mandel interferometric measurements under pulsed pumping without spectral filtering, which indicates excellent frequency indistinguishability between the down-converted photons. The coincident-frequency entanglement source is useful for quantum information processing and quantum measurement applications.Comment: 4 pages, 3 figures, submitted to PR

Efficient generation of tunable photon pairs at 0.8 and 1.6 micrometer

We demonstrate efficient generation of collinearly propagating, highly nondegenerate photon pairs in a periodically-poled lithium niobate cw parametric downconverter with an inferred pair generation rate of 1.4*10^7/s/mW of pump power. Detection of an 800-nm signal photon triggers a thermoelectrically-cooled 20%-efficient InGaAs avalanche photodiode for the detection of the 1600-nm conjugate idler photon. Using single-mode fibers as spatial mode filters, we obtain a signal-conditioned idler-detection probability of about 3.1%.Comment: 8 pages, 3 figure

Single-Photon Frequency Upconversion for Long-Distance Quantum Teleportation and Communication

Thesis Supervisor: Franco N. C. Wong Title: Senior Research Scientist Thesis Supervisor: Jeffrey H. Shapiro Title: Julius A. Stratton Professor of Electrical EngineeringEntanglement generation, single-photon detection, and frequency translation that preserves the polarization quantum state of the photons are essential technologies for long distance quantum communication protocols. This thesis investigates the application of polarization entanglement to quantum communication, including frequency upconversion, photon-counting detection, and photon-pair and entanglement generation. We demonstrate a near-unity efficient frequency conversion scheme that allows fast and efficient photon counting at wavelengths in the low-loss fiberoptic and atmospheric transmission band near 1.55 µm. This upconverter, which is polarizationselective, is useful for classical as well as quantum optical communication. We investigate several schemes that allow frequency translation of polarization-entangled photons generated via spontaneous parametric downconversion in second order nonlinear crystals. We demonstrate upconversion from ∼1.56 to 0.633 µm that preserves the polarization state of an arbitrarily polarized input. The polarization-insensitive upconverter uses bidirectional sum-frequency generation in bulk periodically poled lithium niobate and a Michelson interferometer to stabilize the phase. Using this bidirectional upconversion technique, entangled photons produced in a periodically poled parametric downconverter can be translated to a different wavelength with preservation of their polarization state. We discuss the implications of these results for quantum information processing

Efficient generation of tunable photon pairs at 0.8 and 1.6 pm

We demonstrate efficient generation of collinearly propagating, highly nondegenerate photon pairs in a periodically poled lithium niobate cw parametric downconverter with an inferred pair generation rate of 1.4 3 10 7 ͞s͞mW of pump power. Detection of an 800-nm signal photon triggers a thermoelectrically cooled 20%-efficient InGaAs avalanche photodiode for the detection of the 1600-nm conjugate idler photon. Using single-mode fibers as spatial mode filters, we obtain a signal-conditioned idler-detection probability of ϳ3.1%. © 2002 Optical Society of America OCIS codes: 270.0270, 030.5260, 190.4410, 270.5570. Efficient generation of entangled photons is essential for realizing practical quantum information processing applications such as quantum cryptography and quantum teleportation. Entangled photons are routinely generated by spontaneous parametric downconversion (SPDC) in a nonlinear crystal. 1 More recently, nonlinear waveguides were used for photon pair generation with high eff iciency 2 -4 and better control of the spatial modes. So far, these entangled photon sources have large bandwidths. Recently, a narrowband application was suggested in a singlet-based quantum teleportation system 5 in which narrowband (tens of megahertz) polarization-entangled photons are needed for loading quantum memories that are composed of trapped Rb in optical cavities. 6 Such a narrowband source is most conveniently produced with a resonant cavity such as an optical parametric amplifier (OPA). As a precursor to an OPA configuration, we have studied the generation of collinearly propagating tunable outputs at ϳ800 and ϳ1600 nm in a quasi-phase-matched periodically poled lithium niobate parametric downconverter. Unlike most other SPDC sources, our periodically poled lithium niobate source utilizes a long bulk crystal, which results in a small bandwidth, and the two output wavelengths are widely separated. The choice of wavelengths is designed for loading local Rb-based quantum memories at 795 nm and for low-loss f iber-optic transmission of the conjugate photons at ϳ1.6 mm. The 1600-nm photon can be upconverted via quantum frequency translation 9 for remote quantum memory loading. For the current work, we constructed a compact all-solid-state InGaAs single-photon counter for detecting the 1.6-mm photons. We tested three f iber-pigtailed InGaAs avalanche photodiodes (APDs) from JDS Uniphase (EPM239BA) as passively quenched, gated single-photon counters. -12 Each APD was mounted in a small copper block that was attached to a four-stage thermoelectric cooler, which in turn was in contact with a brass heat sink. We placed this thermoelectric-cooled APD assembly in a sealed box mounted on top of four additional TE coolers for improved temperature control of the APD box. Using this all-solid-state cooling apparatus, we were able to adjust the APD temperature down to 260 ± C without the use of liquid nitrogen. Typically we biased the APDs at 0.2 -1.0 V below the breakdown voltage of the selected APD device, and we applied a gating pulse of 2-4 V to overbias the APDs for single-photon detection. The gate pulses had rise and fall times of 3 -4 ns with subnanosecond timing jitters, and the adjustable pulse length was set at 20 ns. The avalanche output pulses were then amplified by 40 dB with resultant pulse amplitudes of 1-2 V and rise times of less than 2 ns. In general, dark counts increase exponentially with increasing device temperatures, and hence a lower operating temperature is preferred. However, afterpulsing due to trapped charge carriers increases with lower temperatures and also with longer gate durations and higher gate repetition rates. We have found that at an operating temperature of 250 ± C there was negligible afterpulsing for gating frequencies of 100 kHz or less, and the dark counts were low enough to yield a high signal-to-noise ratio (se

Project Staff

The central theme of our programs has been to advance the understanding of optical and quantum communication, radar, and sensing systems. Broadly speaking, this has entailed: (1) developing system-analytic models for important propagation, detection, and communication scenarios; (2) using these models to derive the fundamental limits on system performance; and (3) identifying, and establishing through experimentation the feasibility of, techniques and devices which can be used to approach these performance limits