Non-degenerate Wavelengths Research Articles

Super-resolved quantum ghost imaging

Quantum ghost imaging offers many advantages over classical imaging, including low photon fluxes and non-degenerate object and image wavelengths for imaging light sensitive structures, but suffers from slow image reconstruction speeds. Image reconstruction times depend on the resolution of the required image which scale quadratically with the image resolution. Here, we propose a super-resolved imaging approach based on neural networks where we reconstruct a low resolution image, which we denoise and super-resolve to a high resolution image. To test the approach, we implemented both a generative adversarial network as well as a super-resolving autoencoder in conjunction with an experimental quantum ghost imaging setup, demonstrating its efficacy across a range of object and imaging projective mask types. We achieved super-resolving enhancement of 4times the measured resolution with a fidelity close to 90% at an acquisition time of N^2 measurements, required for a complete N times N pixel image solution. This significant resolution enhancement is a step closer to a common ghost imaging goal, to reconstruct images with the highest resolution and the shortest possible acquisition time.

Molecular Rovibrational Spectroscopy with Undetected Photons via Single-Photon Interferometry

Interferometric spectroscopy with undetected photons (ISUP) utilizing quantum mechanically path-entangled photon pairs has received considerable attention as an optical-measurement platform. Recently, we carried out a proof-of-concept experiment to show that ISUP can be used to measure the transmission spectrum of a Fabry-Perot resonator. Here, we demonstrate that ISUP with dual stimulated parametric down-conversion (StPDC) processes, which allows us to perform infrared rovibrational spectroscopy with visible photons. In our ISUP method, quantum coherence between two independent signal photons from each StPDC crystal is induced by the indistinguishability of conjugate idler fields and results in high visibility of the signal single-photon interferometry at the nondegenerate wavelength. If the seed-beam intensity is imbalanced due to the sample absorption, the corresponding envelope modulation of the interference fringe as a function of the seed-beam frequency reveals the absorption spectrum of the optical sample. As a proof-of-principle experiment, the full rovibrational transmission spectrum at 1550 nm of the hydrogen cyanide (${\mathrm{H}}^{13}{\mathrm{C}}^{14}\mathrm{N}$) molecules in a gas cell is measured from the single-photon interference fringe of the signal fields at 807 nm. We thus anticipate that the single-photon ISUP technique with dual StPDC crystals will find broad use for the development of high-resolution atomic and molecular spectroscopy with undetected photons.

Non-degenerate wavelength computational ghost imaging with thermal light.

Non-degenerate wavelength computational ghost imaging with thermal light source is studied theoretically and experimentally. The acquired computational ghost images are of high quality when the wavelength of computed light is different from the light detected by bucket detector. Compared to the necessary light of short wavelength in previous ghost imaging, the use of longer wavelength light is demonstrated to bring about ghost images with higher spatial resolution, in strong atmospheric turbulence.

Pseudo color ghost coding imaging with pseudo thermal light

We present a new pseudo color imaging scheme named pseudo color ghost coding imaging based on ghost imaging but with multiwavelength source modulated by a spatial light modulator. Compared with conventional pseudo color imaging where there is no nondegenerate wavelength spatial correlations resulting in extra monochromatic images, the degenerate wavelength and nondegenerate wavelength spatial correlations between the idle beam and signal beam can be obtained simultaneously. This scheme can obtain more colorful image with higher quality than that in conventional pseudo color coding techniques. More importantly, a significant advantage of the scheme compared to the conventional pseudo color coding imaging techniques is the image with different colors can be obtained without changing the light source and spatial filter.

Tunable broadband intense IR pulse generation at non-degenerate wavelengths using group delay compensation in a dual-crystal OPA scheme.

A robust group delay compensated dual-crystal optical parametric amplification (DOPA) scheme is proposed that will be used to prove the positive effect of group delay compensation on a DOPA as predicted by the simulations in the previously published literature. Through simple adjustments, it is also capable of providing 20 fs pulses (theoretically compressible to 12 fs, corresponding to sub-four-cycle for 1300 nm components), broadband IR pulses at non-degenerate wavelengths using short pulse (broadband) pump laser. In our table-top DOPA system, group delay compensation has been realized using a simple optical crystal. Our design provides output power in order of 100 mW. We managed to achieve minimum 20 nm improvement on the bandwidth, compared to single-crystal OPA (SOPA) structure whilst keeping total conversion efficiency above 30%. Adjusting our configuration by optimizing the phase-matching angles of the two BBO crystals, we also have realized a practical scheme that benefitting from group delay compensation can obtain 75 nm bandwidth improvement while keeping the conversion efficiency constant. This achievement will open the doors to the realm of multiple crystals OPA systems and provide a solution to the imposed limitation on the effective lengths of applicable non-linear crystals and hence limited power gain of such broadband OPA systems.

Coupling of Whispering-Gallery Modes in the Graphene Nanodisk Plasmonic Dimers

In this paper, we proposed plasmonic dimers consisted of two evanescent field coupled graphene monolayer nanodisks. The electromagnetic properties including the split modes with non-degenerate wavelengths, enhancement of the quality factors (Q factors) and mode areas, and the coupling between the fundamental and the first-order whispering-gallery modes are numerically predicted and analyzed systematically. Compared with the single graphene nanodisk, the Q factor of TM4,1 reaches 356 in a dimer with a radius of 5 nm of each nanodisk and an inter-disk gap of 0.4 nm, where the corresponding mode area is as small as 6.88 × 10‐ 5(λ 0)2. In addition, the enhanced performances of size-mismatched coupled graphene plasmonic dimers are investigated. This graphene monolayer plasmonic dimer could be one of the fundamental components in the future ultra-high density plasmonic circuit technique, on-chip plasmonic interconnect, and transformation plasmonics. It also could be used as the test-beds for added explorations of cavity quantum electrodynamic experiments.

Phase-stable source of polarization-entangled photons in a linear double-pass configuration

We demonstrate a compact, robust, and highly efficient source of polarization-entangled photons, based on linear bi-directional down-conversion in a novel 'folded sandwich' configuration. Bi-directionally pumping a single periodically poled KTiOPO(4) (ppKTP) crystal with a 405-nm laser diode, we generate entangled photon pairs at the non-degenerate wavelengths 784 nm (signal) and 839 nm (idler), and achieve an unprecedented detection rate of 11.8 kcps for 10.4 μW of pump power (1.1 million pairs / mW), in a 2.9-nm bandwidth, while maintaining a very high two-photon entanglement quality, with a Bell-state fidelity of 99.3 ± 0.3%.

Compact dual-crystal optical parametric amplification for broadband IR pulse generation using a collinear geometry

A novel compact dual-crystal optical parametric amplification (DOPA) scheme, collinearly pumped by a Ti:sapphire laser (0.8 μm), is theoretically investigated for efficiently generating broadband IR pulses at non-degenerate wavelengths (1.2 μm~1.4 μm and 1.8 μm~2.1 μm). By inserting a pair of barium fluoride (BaF(2)) wedges between two thin β-barium borate (BBO) crystals, the group velocity mismatch (GVM) between the three interacting pulses can be compensated simultaneously. In this case, the obtained signal spectrum centered at 1.3 μm is nearly 20% broader and the conversion efficiency is increased, but also the pulse contrast and beam quality are improved due to the better temporal overlap. Furthermore, sub-two-cycle idler pulses with carrier-envelope phase (CEP) fluctuation of sub-100-mrad root mean square (RMS) can be generated. Because a tunable few-cycle IR pulse with millijoule energy is attainable in this scheme, it will contribute to ultrafast community and be particularly useful as a driving or controlling field for the generation of ultrafast coherent x-ray supercontinuum.

A single-crystal source of path-polarization entangled photons at non-degenerate wavelengths

We demonstrate a bright, narrowband, compact, quasi-phase-matched single-crystal source generating path-polarization-entangled photon pairs at 810 nm and 1550 nm at a maximum rate of 3 x 10(6) s(-1) THz(-1) mW(-1) after coupling to single-mode fiber, and with two-photon interference visibility above 90%. While the source can already be used to implement quantum communication protocols such as quantum key distribution, this work is also instrumental for narrowband applications such as entanglement transfer from photonic to atomic qubits, or entanglement of photons from independent sources.

Collinear source of polarization-entangled photon pairs at nondegenerate wavelengths

We report on a simple but highly efficient source of polarization-entangled photon pairs at nondegenerate wavelengths. The fully collinear configuration of the source enables very high coupling efficiency into a single optical mode and allows the use of long nonlinear crystals. With optimized dispersion compensation, it is possible to use a free-running laser diode as pump source and to reach an entanglement fidelity of 99.4% at rates as high as 27000pairs∕s∕mW of pump power.

Theory and experiment of entanglement in a quasi-phase-matched two-crystal source

We report results regarding a source of polarization entangled photon pairs created by the process of spontaneous parametric downconversion in two orthogonally oriented, periodically poled, bulk ${\mathrm{KTiOPO}}_{4}$ crystals. The source emits light colinearly at the nondegenerate wavelengths of 810 and $1550\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, and is optimized for a single-mode optical fiber collection and long-distance quantum communication. The configuration favors long crystals, which promote a high photon-pair production rate at a narrow bandwidth, together with a high pair probability in fibers. The quality of entanglement is limited by chromatic dispersion, which we analyze by determining the output state. We find that such a decoherence effect is strongly material dependent, providing for long crystals an upper bound on the visibility of the coincidence fringes of 41% for ${\mathrm{KTiOPO}}_{4}$, and zero for ${\mathrm{LiNbO}}_{3}$. The best obtained raw visibility, when canceling decoherence with an extra piece of crystal, was $91\ifmmode\pm\else\textpm\fi{}0.2%$, including background counts. We confirm by a violation of the CHSH-inequality ($S=2.679\ifmmode\pm\else\textpm\fi{}0.004$ at $55\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1∕2}$ standard deviations) and by complete quantum state tomography that the fibers carry high-quality entangled pairs at a maximum rate of $55\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{THz}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{mW}}^{\ensuremath{-}1}$.

Remote State Preparation: Arbitrary Remote Control of Photon Polarization

We experimentally demonstrate the first remote state preparation of arbitrary single-qubit states, encoded in the polarization of photons generated by spontaneous parametric down-conversion. Utilizing degenerate and nondegenerate wavelength entangled sources, we remotely prepare arbitrary states at two wavelengths. Further, we derive theoretical bounds on the states that may be remotely prepared for given two-qubit resources.

Intersubband second-harmonic generation with voltage-controlled phase matching

We propose an intersubband-based frequency-mixing device in which phase matching is imposed electrically. The dynamic tuning considerably relaxes fabrication tolerances, allows compensation for the intensity dependence of the index, and enables phase-matched operation at a range of degenerate and nondegenerate pump wavelengths.