Quantum frequency conversion (QFC) of photonic signals preserves quantum information while simultaneously changing the signal wavelength. A common application of QFC is to translate the wavelength of a signal compatible with the current fiber-optic infrastructure to a shorter wavelength more compatible with high quality single-photon detectors and optical memories. Recent work has investigated the use of QFC to manipulate and measure specific temporal modes (TMs) through tailoring of the pump pulses. Such a scheme holds promise for multidimensional quantum state manipulation that is both low loss and re-programmable on a fast time scale. We demonstrate the first QFC temporal mode sorting system in a four-dimensional Hilbert space, achieving a conversion efficiency and mode separability as high as 92% and 0.84, respectively. A 20-GHz pulse train is projected onto 6 different TMs, including superposition states, and mode separability with weak coherent signals is verified via photon counting. Such ultrafast high-dimensional photonic signals could enable long-distance quantum communication with high rates.© [2016] [Optical Society of America] One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited. MotivationLong distance quantum-optical communication is indispensable to several applied quantum technologies, such as quantum cryptography [1,2], quantum teleportation [3], and distributed quantum computation [4,5]. It also plays a vital role in the verification of fundamental tenets of physics such as tests of Bell nonlocality [6,7] and relativistic quantum information [8].Ultrafast pulses [9] produced by optical frequency combs (OFCs) with combline spacing in the 10 − 100 GHz regime routinely enable classical communication tasks such as optical networking and signal processing [10][11][12]. Their rich spectral mode structure also offers high-capacity quantum information encoding via multimode quantum states. Availability of sources and tools to exercise control over the mode structure at the transmitter, low loss and noise conditions during propagation through the optical channel, and high mode-separability and detection efficiency at the receiver then become the requisites for large-throughput quantum communication over long distances.One of the most extensively studied sources for high-dimensional information coding at the quantum level are the temporal modes (TMs) of ultrafast quantum states [13,14]. They are typically obtained by carefully engineering the process of spontaneous parametric down conversion (SPDC) or four wave mixing in nonlinear media [15][16][17]. If produced in the telecom wavelength regime, and in a spatial mode compatible with fibers, such multimode quantum signals are also easily integrable with the fiber-optic infrastructure. This ensures that the loss and noise incurred in propagation over lon...

We describe a technique for dynamic quantum optical arbitrary-waveform generation and manipulation, which is capable of mode selectively operating on quantum signals without inducing significant loss or decoherence. It is built upon combining the developed tools of quantum frequency conversion and optical arbitrary waveform generation. Considering realistic parameters, we propose and analyze applications such as programmable reshaping of picosecond-scale temporal modes, selective frequency conversion of any one or superposition of those modes, and mode-resolved photon counting. We also report on experimental progress to distinguish two overlapping, orthogonal temporal modes, demonstrating over 8 dB extinction between picosecond-scale time-frequency modes, which agrees well with our theory. Our theoretical and experimental progress, as a whole, points to an enabling optical technique for various applications such as ultradense quantum coding, unity-efficiency cavity-atom quantum memories, and high-speed quantum computing.

A large format 1k×1k focal plane array (FPA) is realized using type-II superlattice photodiodes for long wavelength infrared detection. Material growth on a 3 in. GaSb substrate exhibits a 50% cutoff wavelength of 11 μm across the entire wafer. The FPA shows excellent imaging. Noise equivalent temperature differences of 23.6 mK at 81 K and 22.5 mK at 68 K are achieved with an integration time of 0.13 ms, a 300 K background and f/4 optics. We report a dark current density of 3.3×10−4 A cm−2 and differential resistance-area product at zero bias R0A of 166 Ω cm2 at 81 K, and 5.1×10−5 A cm−2 and 1286 Ω cm2, respectively, at 68 K. The quantum efficiency obtained is 78%.

We present a hybrid fiber/waveguide design for a 100-MHz frequency comb that is fully self-referenced and temperature controlled with less than 5 W of electrical power. Selfreferencing is achieved by supercontinuum generation in a silicon nitride waveguide, which requires much lower pulse energies (~200 pJ) than with highly nonlinear fiber. These lowenergy pulses are achieved with an erbium fiber oscillator/amplifier pumped by two 250-mW passively-cooled pump diodes that consume less than 5 W of electrical power. The temperature tuning of the oscillator, necessary to stabilize the repetition rate in the presence of environmental temperature changes, is achieved by resistive heating of a section of goldpalladium-coated fiber within the laser cavity. By heating only the small thermal mass of the fiber, the repetition rate is tuned over 4.2 kHz (corresponding to an effective temperature change of 4.2 °C) with a fast time constant of 0.5 s, at a low power consumption of 0.077 W/°C, compared to 2.5 W/°C in the conventional 200-MHz comb design.

We demonstrate frequency-comb-based optical two-way time-frequency transfer across a three-node clock network. A fielded, bidirectional relay node connects laboratory-based master and end nodes, allowing the network to span 28 km of turbulent outdoor air while keeping optical transmit powers below 5 mW. Despite the comparatively high instability of the free-running local oscillator at the relay node, the network transfers frequency with fractional precision below 10−18 at averaging times above 200 s and transfers time with a time deviation below 1 fs at averaging times between 1 s and 1 h. The successful operation of this network represents a promising step toward the operation of future free-space networks of optical atomic clocks.