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Single photon path entangled states for quantum communication

Do Rego Monteiro, Fernando Henrique

Published Jan 1, 2016• 0 citations
Publisher

Abstract

The main work done along my PhD is related to entangled states composed of a single photon. This state generation requires fewer resources when compared to other entangled states generation. Moreover, it's easily scaled to multipartite scenarios and is also robust to setup inefficiencies of quantum repeaters. Our first work with this state was related to its generation and detection, encouraging us to pursue more evidences that this state is useful for quantum communication. The following project was related to demonstrate how this state can be used in a semi-device independent scenario. Our last project regards the use of a heralded photon amplifier that is intended to compensate the loss that is present during state distribution. All these advances makes us confident that this kind of state can find its application in quantum communication, and also encourage us to pursue new practical implementations such as device independent quantum key distribution.

DOI
10.13097/archive-ouverte/unige:89599

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The main work done along my PhD is related to entangled states composed of a single photon. This state generation requires fewer resources when compared to other entangled states generation. Moreover, it's easily scaled to multipartite scenarios and is also robust to setup inefficiencies of quantum repeaters. Our first work with this state was related to its generation and detection, encouraging us to pursue more evidences that this state is useful for quantum communication. The following project was related to demonstrate how this state can be used in a semi-device independent scenario. Our last project regards the use of a heralded photon amplifier that is intended to compensate the loss that is present during state distribution. All these advances makes us confident that this kind of state can find its application in quantum communication, and also encourage us to pursue new practical implementations such as device independent quantum key distribution.
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Optical quantum systems are ideal for testing quantum mechanical laws, but they also find many uses into possible applications to our everyday life related to quantum information science, such as quantum key distribution (QKD) or, in general, quantum communication. Nonlinear and quantum optics and their applications both to quantum communication and to tests of fundamental physics are described in this Thesis. In particular, we have developed and characterised heralded single photon sources at telecommunication wavelengths (1550 nm), based on nonlinear interactions of the second order between electric fields in dielectric materials. This is the starting point for the preparation of single photon entangled states, that we used as a resource for heralded amplification of photonic qubits, with a direct application in Device Independent Quantum Key Distribution (DIQKD) protocols, but also for testing fundamental questions in quantum physics, demonstrating the presence of entanglement in a state that counts a macroscopic number of particles, 500 photons.
One of the main issues in the domain of quantum information and communication is the generation, manipulation and detection of several qubits on a single chip. Several approaches are currently investigated for the implementation of qubits on different types of physical supports and a variety of quantum information technologies are under development: for quantum memories, spectacular advances have been done on trapped atoms and ions, while to transmit information, photons are the ideal support thanks to their high speed of propagation and their almost immunity against decoherence. My thesis work has been focused on the conception, fabrication and characterization of a miniaturized semiconductor source of entangled photons, working at room temperature and telecom wavelengths. First the theoretical concepts relevant to understand the work are described (chapter 1). Then the conception and fabrication procedures are given (chapter 2). Chapter 3 presents the optoelectronics characterization of the device under electrical pumping, and chapter 4 the results on the optical losses measurements and the nonlinear optical characterization (second harmonic generation, spontaneous parametric down conversion and joint spectral intensity reconstruction). Chapters 5 and 6 focus on the characterization of the quantum state generated by a passive sample (demonstration of indistinguishability and energy-time entanglement) and its utilization in a multi- user quantum key distribution protocol (polarization entanglement). Finally the work on the first electrically driven photon pairs source emitting in the telecom range and working at room temperature is presented (chapter 7).
Distributing entangled states over potentially long distances provides a key resource for many protocols in quantum communication and quantum cryptography. Ideally, this should be implemented in a heralded manner. Starting with four single-photon states, we cascade two single-photon path-entangled states, coded in orthogonal polarizations, to distribute and herald polarization entanglement in a single quantum repeater link architecture. By tuning the input states to minimize (local) losses, the theoretically achievable fidelity to the target state without postselection approaches 1, while sacrificing heralding rates. We achieve a fidelity to the target state of over 95% after postselection, providing a benchmark for the experimental control and allowing a first demonstration of a device-independent quantum key distribution architecture capable of operation over relevant distances. We show that the fidelity of the heralded state without postselection scales predictably and also identify various practical challenges and error sources specific to this architecture, and model their effects on the generated state. While our experiment uses probabilistic photon-pair sources based on spontaneous parametric downconversion, many of these problems are also relevant for variants employing deterministic photon sources.