Vesselin G. Velev

Quantum optical arbitrary waveform manipulation and measurement in real time

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.

Multichannel photon-pair generation using hydrogenated amorphous silicon waveguides

We demonstrate highly efficient photon-pair generation using an 8 mm long hydrogenated amorphous silicon (a-Si:H) waveguide in far-detuned multiple wavelength channels simultaneously, measuring a coincidence-to-accidental ratio as high as 400. We also characterize the contamination from Raman scattering and show it to be insignificant over a spectrum span of at least 5 THz. Our results highlight a-Si:H as a potential high-performance, CMOS-compatible platform for large-scale quantum applications, particularly those based on the use of multiplexed quantum signals.

Quantum frequency conversion in nonlinear microcavities

We study nonlinear microresonantors as potential implements for quantum frequency conversion of narrowband optical signals. Using silicon-nitride microdisks as a concrete example, we show that high-conversion performance can be achieved with relatively low pump power. Being chip integratable, such devices hold promise for use in large-scale quantum applications, including atomic-memory-based quantum repeaters.

Inverse-Designed Broadband All-Dielectric Electromagnetic Metadevices

This paper presents a platform combining an inverse electromagnetic design computational method with additive manufacturing to design and fabricate all-dielectric metadevices. As opposed to conventional flat metasurface-based devices that are composed of resonant building blocks resulting in narrow band operation, the proposed design approach creates non-resonant, broadband (Δλ/λ up to >50%) metadevices based on low-index dielectric materials. High-efficiency (transmission >60%), thin (≤2λ) metadevices capable of polarization splitting, beam bending, and focusing are proposed. Experimental demonstrations are performed at millimeter-wave frequencies using 3D-printed devices. The proposed platform can be readily applied to the design and fabrication of electromagnetic and photonic metadevices spanning microwave to optical frequencies.

Selective manipulation of overlapping quantum modes

We show that spatiotemporally overlapping quantum photonic signals in orthogonal time-frequency modes can be discriminated via quantum frequency conversion during a single passage through a waveguide.

Inverse-designed stretchable metalens with tunable focal distance

In this paper we present an inverse-designed 3D-printed all-dielectric stretchable millimeter wave metalens with a tunable focal distance. Computational inverse-design method is used to design a flat metalens made of disconnected building polymer blocks with complex shapes, as opposed to conventional monolithic lenses. Proposed metalens provides better performance than a conventional Fresnel lens, using lesser amount of material and enabling larger focal distance tunability. The metalens is fabricated using a commercial 3D-printer and attached to a stretchable platform. Measurements and simulations show that focal distance can be tuned by a factor of 4 with a stretching factor of only 75%, a nearly diffraction-limited focal spot, and with a 70% focusing efficiency. The proposed platform can be extended for design and fabrication of multiple electromagnetic devices working from visible to microwave radiation depending on scaling of the devices.

Spectrally Multiplexed Upconversion Single-Photon Detection with C-band Pump and Signal Wavelengths

We demonstrate low noise, spectrally multiplexed, upconversion single-photon detection using a waveguide with multiple phase-matching peaks. Two signal wavelengths are upconverted using two distinct pump wavelengths, all in the 1550-nm band.

Phase matching for the optical frequency conversion processes in whispering gallery mode resonators

Optical nonlinear processes in whispering gallery mode resonators require the phase matching that is profoundly different from that in bulk crystals or waveguides. We analyze the phase matching conditions for frequency doubling and parametric down conversion in the resonators, and find the configurations allowing for simultaneous occurrence of these two processes. Such double phase matching gives us access to a variety of interesting quantum nonlinear optical phenomena. For example, it can lead to antibunched emission of photon pairs through the quantum Zeno photonic blockade.

High-speed quantum communications in telecom fibers using overlapping temporal modes

We analyze an efficient quantum-communications architecture over telecom fibers using overlapping time-frequency modes and optimal receivers based on nonlinear processing.