Quantification of the Impact of Photon Distinguishability on Measurement-Device- Independent Quantum Key Distribution

Measurement-Device-Independent Quantum Key Distribution (MDI-QKD) is a two-photon protocol devised to eliminate eavesdropping attacks that interrogate or control the detector in realized quantum key distribution systems. In MDI-QKD, the measurements are carried out by an untrusted third party, and the measurement results are announced openly. Knowledge or control of the measurement results gives the third party no information about the secret key. Error-free implementation of the MDI-QKD protocol requires the crypto-communicating parties, Alice and Bob, to independently prepare and transmit single photons that are physically indistinguishable, with the possible exception of their polarization states. In this paper, we apply the formalism of quantum optics and Monte Carlo simulations to quantify the impact of small errors in wavelength, bandwidth, polarization and timing between Alice’s photons and Bob’s photons on the MDI-QKD quantum bit error rate (QBER). Using published single-photon source characteristics from two-photon interference experiments as a test case, our simulations predict that the finite tolerances of these sources contribute (4.04±20/√Nsifted )% to the QBER in an MDI-QKD implementation generating an Nsifted-bit sifted key

Nonclassical Light Generation from III-V and Group-IV Solid-State Cavity Quantum Systems

In this chapter, we present the state-of-the-art in the generation of nonclassical states of light using semiconductor cavity quantum electrodynamics (QED) platforms. Our focus is on the photon blockade effects that enable the generation of indistinguishable photon streams with high purity and efficiency. Starting with the leading platform of InGaAs quantum dots in optical nanocavities, we review the physics of a single quantum emitter strongly coupled to a cavity. Furthermore, we propose a complete model for photon blockade and tunneling in III-V quantum dot cavity QED systems. Turning toward quantum emitters with small inhomogeneous broadening, we propose a direction for novel experiments for nonclassical light generation based on group-IV color-center systems. We present a model of a multi-emitter cavity QED platform, which features richer dressed-states ladder structures, and show how it can offer opportunities for studying new regimes of high-quality photon blockade.Comment: 64 pages, 32 figures, to appear as Chapter 3 in Advances in Atomic Molecular and Optical Physics, Vol. 6

Topological optimization of hybrid quantum key distribution networks

With the growing complexity of quantum key distribution (QKD) network structures, aforehand topology design is of great significance to support a large-number of nodes over a large-spatial area. However, the exclusivity of quantum channels, the limitation of key generation capabilities, the variety of QKD protocols and the necessity of untrusted-relay selection, make the optimal topology design a very complicated task. In this research, a hybrid QKD network is studied for the first time from the perspective of topology, by analyzing the topological differences of various QKD protocols. In addition, to make full use of hybrid networking, an analytical model for optimal topology calculation is proposed, to reach the goal of best secure communication service by optimizing the deployment of various QKD devices and the selection of untrusted-relays under a given cost limit. Plentiful simulation results show that hybrid networking and untrusted-relay selection can bring great performance advantages, and then the universality and effectiveness of the proposed analytical model are verified.Comment: 12 pages, 4 figure

Doctor of Philosophy

dissertationThe synthesis, characterization, and nonclassical optical properties of photonic crystals (PCs) created from naturally occurring biological templates was studied. Biotemplated PCs were created from several different natural structures using sol-gel chemistry methods. PCs were characterized using a combination of reflection spectroscopy, SEM image analysis, three-dimensional structure modeling, photonic band structure calculations, and density of optical states calculations. The effect our PCs had on the density of optical states (DOS) was probed using time correlated single photon counting spectroscopy. By carefully controlling the sol-gel chemistry used in the templating process, it is possible to synthesize hollow silica inverse, solid silica inverse, hollow titania inverse, solid titania inverse, and solid titania replicate structures. The inverse-type structures have the advantage of being accessible through a single templating step, while the titania replica is capable of a predicted full photonic band gap. Each structure was investigated using methods mentioned above. The reliability of reflectance spectroscopy was investigated. It was found that in certain cases, a continuum of structural parameters yield reflections that match photonic band structure calculations. Methods to improve this situation are discussed. When applied to titania inverse opals, it was found that the refractive index could be determined to ±0.05 and the volume fraction to ±0.5%. Accurately determining the refractive index of inverse opals is useful in estimating the refractive index of other PCs made from the same sol-gel. Calculation of the DOS using a combination of MIT's photonic bands package and house-written software was applied to biotemplated photonic crystals. It was found that even partial band gap photonic crystals can greatly modify the DOS. Finally, the rate of spontaneous emission of quantum dots embedded in photonic crystals was measured to indirectly probe the DOS. Three different models were used to extract the lifetime from radiative decay curves. It was found that a log-normal distribution of lifetimes was the most meaningful model. The radiative lifetime of quantum dots embedded in titania photonic crystals replicated from Lamprocyphus augustus was modified by up to a factor of ten, an amount unprecedented in the photonic crystal literature

Advances in Quantum Nonlinear Optics: a nonclassical journey from the optimization of silicon photomultipliers for Quantum Optics to quantum second-harmonic generation

In this thesis, we present our experimental and theoretical work on modern and old topics of Nonlinear Quantum Optics. The thesis is structured as follows. In the first chapter, we provide a general introduction about the basis of this field, in particular about the main concepts and results that will be needed in the following. In the second and third chapters, we explain our research on the role of silicon photomultipliers in Quantum Optics experiments. After a specific characterization of the sensors, we used them to detect nonclassical states of light. Different strategies for the estimation of experimental quantities are suggested. In the fourth chapter, we propose our quantum description for the second-harmonic-generation process, based on well-known perturbative methods. After a general introduction on the state of the art, we immediately dive into the problem by explaining the employed methods and showing our analytical results. Finally, we resume the essence of our achievements and draw our conclusions

NetSquid, a NETwork Simulator for QUantum Information using Discrete events

In order to bring quantum networks into the real world, we would like to determine the requirements of quantum network protocols including the underlying quantum hardware. Because detailed architecture proposals are generally too complex for mathematical analysis, it is natural to employ numerical simulation. Here we introduce NetSquid, the NETwork Simulator for QUantum Information using Discrete events, a discrete-event based platform for simulating all aspects of quantum networks and modular quantum computing systems, ranging from the physical layer and its control plane up to the application level. We study several use cases to showcase NetSquid's power, including detailed physical layer simulations of repeater chains based on nitrogen vacancy centres in diamond as well as atomic ensembles. We also study the control plane of a quantum switch beyond its analytically known regime, and showcase NetSquid's ability to investigate large networks by simulating entanglement distribution over a chain of up to one thousand nodes.Comment: NetSquid is freely available at https://netsquid.org; refined main text section

Advances in Quantum Nonlinear Optics: a nonclassical journey from the optimization of silicon photomultipliers for Quantum Optics to quantum second-harmonic generation

openIn this thesis, we present our experimental and theoretical work on modern and old topics of Nonlinear Quantum Optics. The thesis is structured as follows. In the first chapter, we provide a general introduction about the basis of this field, in particular about the main concepts and results that will be needed in the following. In the second and third chapters, we explain our research on the role of silicon photomultipliers in Quantum Optics experiments. After a specific characterization of the sensors, we used them to detect nonclassical states of light. Different strategies for the estimation of experimental quantities are suggested. In the fourth chapter, we propose our quantum description for the second-harmonic-generation process, based on well-known perturbative methods. After a general introduction on the state of the art, we immediately dive into the problem by explaining the employed methods and showing our analytical results. Finally, we resume the essence of our achievements and draw our conclusions.openFisica e astrofisicaChesi, GiovanniChesi, Giovann

Programmable Quantum Annealers as Noisy Gibbs Samplers

Drawing independent samples from high-dimensional probability distributions represents the major computational bottleneck for modern algorithms, including powerful machine learning frameworks such as deep learning. The quest for discovering larger families of distributions for which sampling can be efficiently realized has inspired an exploration beyond established computing methods and turning to novel physical devices that leverage the principles of quantum computation. Quantum annealing embodies a promising computational paradigm that is intimately related to the complexity of energy landscapes in Gibbs distributions, which relate the probabilities of system states to the energies of these states. Here, we study the sampling properties of physical realizations of quantum annealers which are implemented through programmable lattices of superconducting flux qubits. Comprehensive statistical analysis of the data produced by these quantum machines shows that quantum annealers behave as samplers that generate independent configurations from low-temperature noisy Gibbs distributions. We show that the structure of the output distribution probes the intrinsic physical properties of the quantum device such as effective temperature of individual qubits and magnitude of local qubit noise, which result in a non-linear response function and spurious interactions that are absent in the hardware implementation. We anticipate that our methodology will find widespread use in characterization of future generations of quantum annealers and other emerging analog computing devices.Comment: 6 pages, 4 figures, with 36 pages of Supplementary Informatio