Anjali Agarwal

Continuously active interferometer stabilization and control for time-bin entanglement distribution.

We describe a new method enabling continuous stabilization and fine-level phase control of time-bin entanglement interferometers. Using this technique we demonstrate entangled photon transmission through 50 km of standard single-mode fiber. This technique reuses the entangled-pair generation pump which is co-propagated with the transmitted entangled photons. The co-propagating pump adds minimal noise to the entangled photons which are characterized by measuring a two-photon interference fringe.

Free-space to single-mode collection efficiency enhancement using photonic lanterns

We demonstrate single-mode collection efficiency enhancement for free space optical systems using a photonic lantern to collect scattered infrared light from diffuse objects at far- and near-field distances. A single-mode collection efficiency improvement of ∼8u2009u2009dB is demonstrated in the near-field region relative to standard single-mode fiber. The insertion loss properties of the photonic lantern are also analyzed, and an additional insertion loss penalty is observed for near-field distances when the transmitted beam is collimated. The photonic lantern can be used for coherent detection systems such as light detection and ranging and free-space optical communication with improved collection efficiency and nearly perfect mode matching.

Optical filtering enabled by cascaded parametric amplification

A cascaded parametric amplifier consists of a first parametric amplifier, which amplifies an input signal and generates an idler, which is a copy of the signal, a signal processor, which controls the phases of the signal and idler, and a second parametric amplifier, which combines the signal and idler in a phase-sensitive manner. In this paper, cascaded parametric amplification is modeled and the conditions required to maximize the constructive-destructive extinction ratio are determined. The results show that a cascaded parametric amplifier can be operated as a filter: A desired signal-idler pair is amplified, whereas undesired signal-idler pairs are deamplified. For the desired signal and idler, the noise figures of the filtering process (input signal-to-noise ratio divided by the output ratios) are only slightly higher than those of the copying process: Signal-processing functionality can be achieved with only a minor degradation in signal quality.

Quantum communications with optical phase sensitive amplifiers

We review our recent work exploring the use of phase-sensitive amplification for improving the transmission and detection of quantum signals.

Signal replication by multiple sum- or difference-frequency generation

In this paper, the coupled-mode equations for sum-frequency generation (SFG) and difference-frequency generation (DFG) driven by multiple pumps are solved, and the noise figures of idler generation are determined. For SFG, the (common) noise figure is n, the number of pumps (and idlers), whereas for DFG, the (common) noise figure is 2, independent of n. Thus, DFG driven by multiple pumps enables the generation of multiple low-noise idlers.

Entanglement Transmission through a Distributed Phase Sensitive Amplifier

We demonstrate transmission of entangled photons through a χ(3)-based 5-km distributed optical amplifier operated in the low-gain limit to offset loss. No measurable degradation in entanglement quality is observed after the amplifier.

Performance of Optical Phase Sensitive Amplifiers with Correlated Single Photon Pairs

We consider the performance of an optical phase-sensitive amplifier (OPSA) with correlated single photon pairs. We show that quantum correlations exist after the OPSA, which demonstrates the significance of constructive quantum interference in the OPSA.

Single mode collection efficiency enhancement for free space systems using photonic lantern

We analyze and demonstrate free-space to 19-port photonic lantern light collection efficiency for scattering from diffuse objects. A single-mode collection efficiency improvement of ~8 dB is demonstrated in the near field region.

Hyperentanglement for quantum telecommunications

We describe how hyperentanglement may be used to give orders of magnitude throughput improvement over singly entangled photon pairs, for some applications. Next we demonstrate the first measurement of hyperentangled photon pairs, both of which are at telecom wavelengths, via simultaneous polarization tomography and time-bin interference measurements. Without cryogenic cooling of the nonlinear element, we measure polarization entanglement with tangle of 0.4 ± 0.2 and time bin entanglement with visibility of 83% ± 6%, both exceeding classical thresholds by approximately two standard deviations.

Comparison of LIDAR system performance for alternative single-mode receiver architectures: modeling and experimental validation

In this paper, we describe a detailed performance comparison of alternative single-pixel, single-mode LIDAR architectures including (i) linear-mode APD-based direct-detection, (ii) optically-preamplified PIN receiver, (iii) PINbased coherent-detection, and (iv) Geiger-mode single-photon-APD counting. Such a comparison is useful when considering next-generation LIDAR on a chip, which would allow one to leverage extensive waveguide-based structures and processing elements developed for telecom and apply them to small form-factor sensing applications. Models of four LIDAR transmit and receive systems are described in detail, which include not only the dominant sources of receiver noise commonly assumed in each of the four detection limits, but also additional noise terms present in realistic implementations. These receiver models are validated through the analysis of detection statistics collected from an experimental LIDAR testbed. The receiver is reconfigurable into four modes of operation, while transmit waveforms and channel characteristics are held constant. The use of a diffuse hard target highlights the importance of including speckle noise terms in the overall system analysis. All measurements are done at 1550 nm, which offers multiple system advantages including less stringent eye safety requirements and compatibility with available telecom components, optical amplification, and photonic integration. Ultimately, the experimentally-validated detection statistics can be used as part of an end-to-end system model for projecting rate, range, and resolution performance limits and tradeoffs of alternative integrated LIDAR architectures.