Natalia Bruno

Displacement of entanglement back and forth between the micro and macro domains

We report an experimental observation of heralded entanglement involving two components that can be distinguished with detectors resolving only large photon number differences. We demonstrate entanglement in states containing over 500 photons.

Heralded photon amplification for quantum communication

Heralded noiseless amplification based on single-photon sources and linear optics is ideally suited for long-distance quantum communication tasks based on discrete variables. We experimentally demonstrate such an amplifier, operating at telecommunication wavelengths. Coherent amplification is performed with a gain of G=1.98±0.20 for a state with a maximum expected gain G=2. We also demonstrate that there is no need for a stable phase reference between the initial signal state and the local auxiliary photons used by the amplifier. We discuss these results in the context of experimental device-independent quantum key distribution based on heralded qubit amplification, and we highlight several key challenges for its realization.

High efficiency coupling of photon pairs in practice

Multi-photon and quantum communication experiments such as loophole-free Bell tests and device independent quantum key distribution require entangled photon sources which display high coupling efficiency. In this paper we put forward a simple quantum theoretical model which allows the experimenter to design a source with high pair coupling efficiency. In particular we apply this approach to a situation where high coupling has not been previously obtained: we demonstrate a symmetric coupling efficiency of more than 80% in a highly frequency non-degenerate configuration. Furthermore, we demonstrate this technique in a broad range of configurations, i.e. in continuous wave and pulsed pump regimes, and for different nonlinear crystals.

Integrated AlGaAs source of highly indistinguishable and energy-time entangled photons

The generation of nonclassical states of light in miniature chips is a crucial step toward practical implementations of future quantum technologies. Semiconductor materials are ideal for achieving extremely compact and massively parallel systems and several platforms are currently under development. In this context, spontaneous parametric downconversion in AlGaAs devices combines the advantages of room temperature operation, possibility of electrical injection, and emission in the telecom band. Here we report on a chip-based AlGaAs source, producing indistinguishable and energy-time entangled photons with a brightness of 7.2×106  pairs/s and a signal-to-noise ratio of 141±12. Indistinguishability between the photons is demonstrated via a Hong–Ou–Mandel experiment with a visibility of 89±3%, mainly limited by the reflectivity of the chip facets, while energy-time entanglement is tested via a Franson interferometer leading to a visibility of 96±4.

A complete characterization of the heralded noiseless amplification of photons

Heralded noiseless amplification of photons has recently been shown to provide a means to overcome losses in complex quantum communication tasks. In particular, to overcome transmission losses that could allow for the violation of a Bell inequality free from the detection loophole, for device independent quantum key distribution (DI-QKD). Several implementations of a heralded photon amplifier have been proposed and the first proof of principle experiments realized. Here we present the first full characterization of such a device to test its functional limits and potential for DI- QKD. This device is tested at telecom wavelengths and is shown to be capable of overcoming losses corresponding to a transmission through 20km of single mode telecom fibre. We demonstrate heralded photon amplifier with a gain >100 and a heralding probability >83%, required by DI-QKD protocols that use the Clauser-Horne-Shimony-Holt inequality. The heralded photon amplifier clearly represents a key technology for the realization of DI-QKD in the real world and over typical network distances.

Generation of tunable wavelength coherent states and heralded single photons for quantum optics applications

Abstract Quantum optics experiments frequently involve interfering single photons and coherent states. In the case of multi-photon experiments this requires all photons to be frequency degenerate. We report a simple and practical approach to generate coherent states that can be readily tuned to any wavelength required, for example by non-degenerate photon pair creation. We demonstrate this by performing a two-photon (Hong–Ou–Mandel) interference experiment between a coherent state and a pure heralded single photon source. Neither interfering photon passes through a spectral filter, the coherent state is constrained by the pump and seed lasers and the heralded photon exploits non-local filtering. We expect that such an approach can find a wide range of applications in photonic based quantum information science.

Heralded amplification of photonic qubits

We demonstrate postselection free heralded qubit amplification for Time-Bin qubits and single photon states in an all-fibre, telecom-wavelength, scheme that highlights the simplicity, stability and potential for fully integrated photonic solutions. Exploiting high-efficiency superconducting detectors, the gain, fidelity and the performance of the amplifier are studied as a function of loss. We also demonstrate the first heralded single photon amplifier with independent sources. This provides a significant advance towards demonstrating device-independent quantum key distribution as well as fundamental tests of quantum mechanics over extended distances.

Experimental heralded amplification of time-bin qubits

We present an experimental realisation of heralded amplification of time-bin qubits for quantum communication, based on a source of separable photons at telecom wavelengths, with Hong-Ou-Mandel visibility > 90% without any filtering and high coupling efficiency.

A source of pure photons with high heralding efficiency for amplification of time-bin qubits

We realised a four-photons source in a separable state, shown by Hong-Ou-Mandel interference with visibility >90%. This source is optimal for the implementation of protocols such as the heralded amplification of time-bin qubits.

Single Photons, Entanglement Swapping and Heralded Photon Amplification for Device Independent Quantum Key Distribution

We discuss several key challenges for quantum communication ranging from engineering photon sources through faithful entanglement swapping to heralded photon, or qubit, amplification and their implications for experimental device independent QKD.