[Show abstract][Hide abstract] ABSTRACT: We have developed the technique of two-photon joint temporal density measurements for temporal state characterization, thus facilitating two-photon generation with high temporal entanglement or nearly factorizable outputs by controlling the ultrafast pump bandwidth.
[Show abstract][Hide abstract] ABSTRACT: Recent advances in quantum information processing (QIP) have enabled practical applications of quantum mechanics in various fields such as cryptography, computation, and metrology. Most of these applications use photons as carriers of quantum information. Therefore, engineering the quantum state of photons is essential for the realization of novel QIP schemes. A practical and flexible technique to generate high-purity entangled photon pairs is spontaneous parametric downconversion (SPDC) which finds its use in many QIP applications such as quantum key distribution (QKD) and linear optics quantum computation. SPDC is often used with ultrafast lasers to generate photon pairs with precise timing and engineered spectral properties. In this thesis, we focused on two photonic QIP applications using ultrafastpumped SPDC. We first pursued the design and implementation of a pulsed narrowband polarization-entangled photon pairs at 780nm for free-space entanglement-based QKD. We built and characterized a compact narrowband ultraviolet pump source and a polarization-entangled photon source based on SPDC in a polarization Sagnac interferometer. We then studied the generation of coincident-frequency entangled photons for Heisenberg-limited quantum metrology. Using extended phase-matching conditions in a periodically-poled KTP crystal, generation of coincident-frequency entanglement was verified and frequency indistinguishability was achieved for broadband signal and idler photons at ~1.58 [mu]m. We also developed a novel time domain characterization technique based on time-resolved single-photon upconversion. Using this technique, we measured the joint temporal density of a two-photon state for the first time and observed temporal anti-correlation for the coincident-frequency entangled state as predicted by Fourier duality. This new technique complements existing frequency domain methods for a more complete characterization of two-photon states.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a technique for characterizing two-photon quantum states based on joint temporal correlation measurements using time-resolved single-photon detection by femtosecond up-conversion. We measure for the first time the joint temporal density of a two-photon entangled state, showing clearly the time anticorrelation of the coincident-frequency entangled photon pair generated by ultrafast spontaneous parametric down-conversion under extended phase-matching conditions. The new technique enables us to manipulate the frequency entanglement by varying the down-conversion pump bandwidth to produce a nearly unentangled two-photon state that is expected to yield a heralded single-photon state with a purity of 0.88. The time-domain correlation technique complements existing frequency-domain measurement methods for a more complete characterization of photonic entanglement.
Full-text · Article · Nov 2008 · Physical Review Letters
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a time-resolved single-photon detection technique based on ultrafast sum-frequency generation, providing femtosecond measurement capability for single photons in photonic quantum information processing. Noncollinear broadband upconversion in periodically poled MgO-doped stoichiometric lithium tantalate with an ultrafast pump and detection with a Si single-photon counter enable efficient detection of IR photons and temporal resolution of ~150 fs. We utilize the timing resolution to map the generation efficiency profile along the propagation axis of a periodically poled KTiOPO(4) crystal, revealing its local grating quality with millimeter resolution. We also apply the technique to two-photon coincidence measurements and directly demonstrate time anticorrelation between coincident-frequency entangled photons that are parametrically generated under extended phase-matching conditions.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a new technique of efficient, time-resolved, infrared single-photon detection using noncollinearly phase-matched frequency upconversion by an ultrafast pump, allowing nearly background-free sub-picosecond characterization of 1582-nm time anti-correlated entangled photons.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate pulsed operation of a bidirectionally pumped polarization Sagnac interferometric down-conversion source and its generation of narrow-band, high-visibility polarization-entangled photons. Driven by a narrow-band, mode-locked pump at 390.35 nm, the phase-stable Sagnac source with a type-II phase-matched periodically poled KTiOPO4 crystal is capable of producing 0.01 entangled pair per pulse in a 0.15-nm bandwidth centered at 780.7 nm with 1 mW of average pump power at a repetition rate of 31.1 MHz. We have achieved a mean photon-pair generation rate of as high as 0.7 pair per pulse, at which multipair events dominate and significantly reduce the two-photon quantum-interference visibility. For low generation probability α, the reduced visibility V=1−α is independent of the throughput efficiency and of the polarization analysis basis, which can be utilized to yield an accurate estimate of the generation rate α. At low α we have characterized the source entanglement quality in three different ways: average quantum-interference visibility of 99%, the Clauser-Horne-Shimony-Holt S parameter of 2.739±0.119, and quantum state tomography with 98.85% singlet-state fidelity. The narrow-band pulsed Sagnac source of entangled photons is suitable for use in quantum information processing applications such as free-space quantum key distribution.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a pulsed entanglement source with a flux high enough to reduce quantum-interference visibility due to multiple pairs. An array of such pulsed downconverters can be configured to yield single photons on demand. Article not available.
[Show abstract][Hide abstract] ABSTRACT: We report efficient picosecond UV generation by means of frequency quadrupling of an amplified picosecond fiber laser. This narrowband 390-nm source with 250 mW is suitable for a number of quantum information processing tasks.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a high-power, narrowband pulsed source at 390 nm by two stages of frequency doubling in periodically poled MgO:LiNbO(3) and periodically poled KTiOPO(4) of an amplified, passively mode-locked fiber laser. With a frequency quadrupling efficiency of 5.5% and a 0.1 nm bandwidth, the 250 mW ultraviolet source is a suitable compact pump source for many entanglement-based quantum information processing tasks.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a narrowband pulsed source of polarization-entangled photons based on parametric downconversion in a phase-stable Sagnac interferometer that is suitable for free-space quantum key distribution with high key generation rates.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate efficient picosecond UV generation by means of frequency quadrupling of an amplified picosecond fiber laser. The narrowband 390-nm source with 250 mW is suitable for a number of quantum information processing tasks.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate a source of entangled photon pairs with identical frequency spectra. An Hong-Ou-Mandel interferometric measurement of this source shows a high visibility of 85% under pulsed pumping and without any spectral filtering.
[Show abstract][Hide abstract] ABSTRACT: 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 KTiOPO4. 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.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate optical clockwork without the need for carrier-envelope phase control by use of sum-frequency generation between a continuous-wave optical parametric oscillator at 3.39 microm and a femtosecond mode-locked Ti:sapphire laser with two strong spectral peaks at 834 and 670 nm, a spectral difference matched by the 3.39-microm radiation.
[Show abstract][Hide abstract] ABSTRACT: We demonstrate optical clockwork without carrier-envelope phase control using sum-frequency generation between a cw optical parametric oscillator at 3.39 μm and a mode-locked Ti:sapphire laser with dominant spectral peaks at 834 nm and 670 nm.
[Show abstract][Hide abstract] ABSTRACT: We describe a self-referenced optical frequency comb generator based on an octave-spanning, prismless Ti:sapphire laser. Dispersion compensation is provided by novel double-chirped mirror pairs and BaF2 wedges. Current versions operate at 80 and 150 MHz. The compact prismless design allows system scaling to a gigahertz repetition rate. Its carrier-envelope beat note is intrinsically stable with a signal-to-noise ratio of 30 dB in a 100-kHz bandwidth. The octave is reached at 25 dB below the average power level. The in-loop accumulated phase error is 1.4 rad (20 mHz to 1 MHz). The technique has the advantages of simplicity and stability compared with previous designs.
[Show abstract][Hide abstract] ABSTRACT: We describe a self-referenced optical frequency comb generator based on an octave spanning, prismless Ti:sapphire laser. Current versions operate at 80 MHz and 150 MHz. System scaling to GHz repetition rates is possible
[Show abstract][Hide abstract] ABSTRACT: An octave-spanning, prism-less Ti:sapphire laser is demonstrated based on double-chirped mirror pairs. The Ti:sapphire laser synchronized to a 30 fs Cr:forsterite laser using balanced cross-correlation. A residual timing jitter of a tenth of an optical cycle, i.e. 300 attoseconds is achieved.