Certifying position-momentum entanglement at telecommunication wavelengths
Lukas Achatz, Evelyn A Ortega, Krishna Dovzhik, Rodrigo F Shiozaki, Jorge Fuenzalida, Sören Wengerowsky, Martin Bohmann and Rupert Ursin
Abstract
The successful employment of high-dimensional quantum correlations and its integration in telecommunication infrastructures is vital in cutting-edge quantum technologies for increasing robustness and key generation rate. Position-momentum Einstein-Podolsky-Rosen (EPR) entanglement of photon pairs are a promising resource of such high-dimensional quantum correlations. Here, we experimentally certify EPR correlations of photon pairs generated by spontaneous parametric down-conversion (SPDC) in a nonlinear crystal with type-0 phase-matching at telecommunication wavelength for the first time. To experimentally observe EPR entanglement, we perform scanning measurements in the near- and far-field planes of the signal and idler modes. We certify EPR correlations with high statistical significance of up to 45 standard deviations. Furthermore, we determine the entanglement of formation of our source to be greater than one, indicating a dimensionality of greater than 2. Operating at telecommunication wavelengths around 1550 nm, our source is compatible with today’s deployed telecommunication infrastructure, thus paving the way for integrating sources of high-dimensional entanglement into quantum-communication infrastructures.
Microwave-optical coupling via Rydberg excitons in cuprous oxide
Liam A. P. Gallagher, Joshua P. Rogers, Jon D. Pritchett, Rajan A. Mistry, Danielle Pizzey, Charles S. Adams, Matthew P. A. Jones, Peter Grünwald, Valentin Walther, Chris Hodges, Wolfgang Langbein, and Stephen A. Lynch
Abstract
We report exciton-mediated coupling between microwave and optical fields in cuprous oxide (Cu2O) at low temperatures. Rydberg excitonic states with principal quantum number up to n=12 were observed at 4 K using both one-photon (absorption) and two-photon (second harmonic generation) spectroscopy. Near resonance with an excitonic state, the addition of a microwave field significantly changed the absorption line shape, and added sidebands at the microwave frequency to the coherent second harmonic. Both effects showed a complex dependence on n and angular momentum l. All of these features are in semiquantitative agreement with a model based on intraband electric dipole transitions between Rydberg exciton states. With a simple microwave antenna we already reach a regime where the microwave coupling (Rabi frequency) is comparable to the nonradiatively broadened linewidth of the Rydberg excitons. The results provide an additional way to manipulate excitonic states, and open up the possibility of a cryogenic microwave to optical transducer based on Rydberg excitons.
Unconditionally secure digital signatures implemented in an eight-user quantum network
Yoann Pelet, Ittoop Vergheese Puthoor, Natarajan Venkatachalam, Soren Wengerowsky, Martin Loncari, Sebastian Philipp Neumann, Bo Liu, Zeljko Samec, Mario Stipcevi, Rupert Ursin, Erika Andersson, John G Rarity, Djeylan Aktas and Siddarth Koduru Joshi
Abstract
The ability to know and verifiably demonstrate the origins of messages can often be as important as encrypting the message itself. Here we present an experimental demonstration of an unconditionally secure digital signature (USS) protocol implemented for the first time, to the best of our knowledge, on a fully connected quantum network without trusted nodes. We choose a USS protocol which is secure against forging, repudiation and messages are transferrable. We show the feasibility of unconditionally secure signatures using only bi-partite entangled states distributed throughout the network and experimentally evaluate the performance of the protocol in real world scenarios with varying message lengths.
Ultrabright Sagnac-type source of non-degenerate polarization-entangled photon pairs using only off-the-shelf optical components
Jakub Szlachetka, Kaushik Joarder, Piotr Kolenderski
Abstract
We develop a Sagnac-type source of ultrabright, non-degenerate, polarization-entangled photon pair that is highly stable and compact simultaneously. We use a 20 mm long PPLN bulk crystal which, upon pumping continuously with 532 nm wavelength, produces polarization-entangled photon-pairs of 785 nm signal and 1651 nm idler wavelengths via the type-0 spontaneous parametric down-conversion (SPDC) process. All optical components used in the setup are off-the-shelf components, readily available commercially; hence, no custom-designed or costly multi-wavelength polarization optics are required. At the same time, long-term phase stability is achieved without any additional active stabilization; due to the geometry of our Sagnac-type design. We also report one of the highest brightness of non-degenerate polarization-entangled photon pairs available in the literature. Even with a very low pump power of 0.034 mW, we detect a coincidence rate of (6.96±0.03)×104 entangled pairs/sec/mW (averaged over three polarization-basis measurements: H/V, D/A, and R/L basis). The source’s brightness is calculated to be (6.17±0.04)×106 entangled pairs/sec/mW for the signal line width of 0.4 nm. From the raw coincidence counts (without any background coincidence correction), the fidelity of the entangled state is measured to be (96.72±0.01)% with a concurrence of (94.68±0.20)%. Bell-CHSH inequality violation is reported as S=2.71±0.06.
Edge-enhanced optical parametric generation in periodically poled LiNbO3
Nicklas Bjärnhall Prytz, Daniel Qvarngård, Antti Härkönen, Mircea Guina, and Katia Gallo
Abstract
We demonstrate enhanced optical parametric gains occurring at the edge of periodically poled LiNbO3 (PPLN) regions. Experiments performed in MgO-doped PPLN samples, pumped at 532 nm with parametric signal outputs around 800 nm and 1550 nm, exhibit good agreement with numerical simulations of the nonlinear wave dynamics in the system, based on the assumption of an average refractive index increase Δn = 5.3×10−5 in the PPLN region. Excitation in proximity to the PPLN edge with a pump power of 8.1 mW results in a 3.6-fold output power increase with respect to parametric generation inside the PPLN area.
Single-photon infrared waveguide based upconversion imaging
R. Smith, B. Ndaganoa, G. Redonnet-Brown, A. Weaver, A. Astill, H. White, C. B. E. Gawith, L. J. McKnight
Abstract
We report a nonlinear optical upconversion 3D imaging system for infrared radiation enabled by zinc indiffused MgO:PPLN waveguides. While raster-scanning a scene with an 1800 nm pulsed-laser source, we record time-of-flight information, thus probing the 3D structure of various objects in the scene of interest. Through upconversion, the 3D information is transferred from 1800 nm to 795 nm, a wavelength accessible to single-photon avalanche diode (SPAD).
A Nanosecond Optical Parametric Oscillator in the mid IR Region with Double Pass Pump
D. B. Kolker, M. K. Starikova, R. V. Pustovalova, A. I. Karapuzikov, A. A. Karapuzikov, O. M. Kuznetsov, and Yu. V. Kistenev
Abstract
An optical parametric oscillator (OPO) with double pass pump based on MgO:PPLN and PPLN periodic structures is described. A compact nanosecond Nd:YLF laser has been used as a pump source at 1.053 μm (the pumping pulse duration is 5–7 ns at a maximum pulse energy of 300 μJ at frequencies of 1⎯7 kHz). The oscillation threshold of the OPO based on MgO:PPLN was varied in a range of 11–28 μJ at wavelength of 2.1–4.3 μm. The conversion efficiency from the pump wave to an idler wave decreased from 8.6 to 2.5% in the range of 2.0–4.3 μm. For PPLN OPO the measured threshold was 36 μJ at 4.2 μm and 49 μJ at 4.7 μm. The conversion efficiency of the pump energy into the energy of an idler wave was 3.3–0.4% at wavelengths of 4.2⎯4.7 μm.
Compact picosecond mid-IR PPLN OPO with controllable peak powers
Yudi Wu, Sijing Liang, Qiang Fu, Lin Xu, and David J. Richardson
Abstract
We report a high-repetition-rate, compact, mid-infrared picosecond (ps) optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN). The OPO is synchronously pumped by an ytterbium-doped-fibre (YDF) master-oscillator-power-amplifier (MOPA) system, seeded by a 1040-nm gain-switched laser diode (GSLD). Under continuous-wave (cw) pulsed operation, at a 1.5-GHz repetition rate and 14-Wpump power, an idler average power of 2.4 W (30 W peak power) was achieved, with an idler wavelength tunability of 2260–3573 nm. Through the addition of an electro-optic modulator (EOM) to the MOPA system, acting as a time gate to suppress a variable number of pulses per 1 μs, a quasi-cw pumping regime was realized, allowing burst-mode operation of the OPO at a 1-MHz inter-burst repetition rate. By varying the burst window time with the EOM, controllable idler peak powers of up to 1.2 kW were then realized.
Quasi-CW Pumping of a Single-Frequency Fiber Amplifier for Efficient SHG in PPLN Crystals with Reduced Thermal Load
Enkeleda Balliu ,Magnus Engholm, Michel J. F. Digonnet and Hans-Erik Nilsson
Abstract
Single-frequency lasers are essential for high-resolution spectroscopy and sensing applications as they combine high-frequency stability with low noise and high output power stability. For many of these applications, there is increasing interest in power-scaling single-frequency sources, both in the near-infrared and visible spectral range. We report the second-harmonic generation of 670 µJ at 532 nm of a single-frequency fiber amplifier signal operating in the quasi-continuous-wave mode in a 10-mm periodically poled Mg-doped lithium niobate (MgO:PPLN) crystal, while increasing compactness. To the best of our knowledge, this is the highest pulse energy generated in this crystal, which may find applications in the visible and UV such as remote Raman spectroscopy.
Mid-infrared coincidence measurements on twin photons at room temperature
M. Mancinelli, A. Trenti, S. Piccione, G. Fontana, J.S. Dam, P. Tidemand-Lichtenberg, C. Pedersen & L. Pavesi
Abstract
Quantum measurements using single-photon detectors are opening interesting new perspectives in diverse fields such as remote sensing, quantum cryptography and quantum computing. A particularly demanding class of applications relies on the simultaneous detection of correlated single photons. In the visible and near infrared wavelength ranges suitable single-photon detectors do exist. However, low detector quantum efficiency or excessive noise has hampered their mid-infrared (MIR) counterpart. Fast and highly efficient single-photon detectors are thus highly sought after for MIR applications. Here we pave the way to quantum measurements in the MIR by the demonstration of a room temperature coincidence measurement with non-degenerate twin photons at about 3.1 mm. The experiment is based on the spectral translation of MIR radiation into the visible region, by means of efficient up-converter modules. The up-converted pairs are then detected with low-noise silicon avalanche photodiodes without the need for cryogenic cooling.
