Abstract Nowadays the fields of Quantum Optics and Quantum Information are experiencing a mayor development worldwide, in particular, in the experimental arena. The reason relies in the high perspectives of application of these fields in areas as computing, security, telecommunications and metrology, among others. A determinant fact for the experimental and technological development is the ability to design and construct electronic devices suitable for the study of light with quantum features, as well as the software which is necessary for the analysis and processing of experimental data. In this work we present a general overview of the theory, practical design and experimental tests of one of such devices called Homodyne Detector addressed to the study and engineering of quantum states of light.
Abstract Nowadays the fields of Quantum Optics and Quantum Information are experiencing a mayor development worldwide, in particular, in the experimental arena. The reason relies in the high perspectives of application of these fields in areas as computing, security, telecommunications and metrology, among others. A determinant fact for the experimental and technological development is the ability to design and construct electronic devices suitable for the study of light with quantum features, as well as the software which is necessary for the analysis and processing of experimental data. In this work we present a general overview of the theory, practical design and experimental tests of one of such devices called Homodyne Detector addressed to the study and engineering of quantum states of light.
Generation and measurement of quantum states of the electromagnetic field represent a hot and widely discussed topic in the Physics community, since optical states are useful not only in fundamental experiments but also in several applications in the fields of Quantum Optics and Quantum Information (Bouwmeester et al., 2000). In fact, optical radiation is endowed with relevant characteristics as it travels at maximum possible speed, it is almost unaffected by the interaction with the environment, which in many cases represents an unavoidable decoherence source, and it can be integrated in optoelectronic circuits to implement quantum computing protocols (Sansoni et al., 2010). The possibility of using optical fields in applicative protocols depends on the capability of generating and manipulating optical states that are robust with respect to losses (i.e. that contain a sizeable number of photons) and that can be produced and measured at high rate. For all these reasons, mesoscopic pulsed optical states containing few tens of photons per pulse seem to be the ideal candidates for applications to quantum communication protocols in which each pulse must be addressed individually. Moreover, the problem of generating suitable pulsed states must be considered together with the question of their measurement and characterization. In fact, nowadays we have many types of pulsed-light sources at our disposal, each of them characterized by different pulse durations (from few fs up to few ns), different pulse-repetition rates (from few Hz to 100 MHz) and a wide range of energies per pulse (from few nJ to several J). However, not all these pulsed light can be easily measured. In the mesoscopic intensity regime, for example, detectors endowed with photon-number resolution are required so as to determine shot-by-shot photon numbers or, at least, to characterize some features of the optical states. In fact, full characterization of the optical state, obtained e.g. by evaluating its Wigner function, can be achieved with optical homodyne tomography (OHT) (Raymer, 1997), a technique that over the years has proved its effectiveness in reconstructing both classical and quantum states, even if further optimizations are needed in the case of pulsed fields (Zavatta et al., 2006). Direct detection schemes are an alternative to OHT in all the cases in which knowing the statistics of detected photons is sufficient to characterize the signal state, as demonstrated in the pioneering work of Arecchi (Arecchi, 1965). Obviously, the implementation of a direct detection scheme requires a proper choice of the detector, the development of a calibration 11
Generation and measurement of quantum states of light represent a hot and widely discussed topic in the physical community for their possible applications to quantum optics and quantum information. To this aim, it is desirable that optical states are robust with respect to losses and can be produced and addressed at high rates. In fact, mesoscopic pulsed optical states containing few photons per pulse seem to be the ideal candidates for applications to quantum communication protocols. For all these reasons, during the last two decades many efforts have been devoted to the development of new kinds of detectors that can operate in such a photon-number-resolving domain.
Quantum optics has successfully been used to test fundamental principles in quantum physics and to demonstrate the potential of quantum-enhanced technologies. Linear quantum optics, in which large quantum states of light are produced by optical interference of smaller quantum states, has proved to be particularly fruitful. Further progress will rely both on developing improved experimental tools to manipulate and measure quantum light, and on expanding and refining the range of applications of these technologies. This thesis presents our contributions towards both of these endeavours. We first focus on some of the components necessary for linear quantum optics, starting with the requirement for reconfigurable interference between several optical modes. We propose a novel design for interferometers that satisfy this requirement, which is based on a new mathematical decomposition of unitary matrices used to describe optical interference. We show that our design is more efficient than previously known designs. We also experimentally demonstrate a modular approach to building these devices, which is based on the assembly of multiple UV-written integrated photonic chips. These chips are characterised, and three of them are assembled into a structure shown to enable a wide range of optical transformations. We then study methods of photon detection, showing how photon detectors can be calibrated and discussing the operation of superconducting photon number resolving transition edge sensors. Next, we study two applications of linear optics. We examine the applicability of a proposal for simulating molecular spectroscopy using quantum optics in the presence of experimental imperfections. Our findings are illustrated with a proof of principle experiment in which we simulate part of the vibronic spectrum of the tropolone molecule. Finally, we study a class of optical devices, known as optical Ising machines, that has been shown to find solutions to difficult combinatorial problems. Describing the optical pulses in these devices in phase space as Gaussian quasi-probability distributions that evolve stochastically, we analyse the computational mechanism of these machines and show in theory that they can be simplified without affecting their performance.
The Continuous-variable quantum key distribution (CVQKD) technique is one of the practical uses of quantum information technology. CVQKD system is implemented based on existing optical networks and standard telecommunication technologies. CVQKD can be put into use of the information transmission in city-based areas, within the extent of absolute security and without any restrictions of security. To reduce the experimental system to a commercial prototype, a data acquisition (DAQ) card can be used to replace the DAQ equipment in the laboratory. It can save the cost of the system experiment and commercial application. In this paper, through the high-speed DAQ card, we implement the collection and uploading of the electrical signal, when the light passes through the continuous optical coherent state detector. The whole experiment test system consists of a field-programmable gate array (FPGA), an analog-to-digital converter (ADC) chip, and optical components. This paper provides a method of gain adjustment of the balanced homodyne detector and a way to test the π phase voltage of the optical modulator. The results show that the DAQ card can be used in the development of the CVQKD prototype.
Summary form only given. The ability to engineer various quantum states of light is a central requirement for quantum information processing, including quantum communication, computing and metrology. In this endeavor, many experiments use the so-called conditional preparation technique. The dynamic of the heralded states, i.e. its temporal mode, mainly depends on the setup and has been studied theoretically with different strategies [1,2]. However, it remains difficult to extract the optimal mode with a precise description of the experimental setup: it requires very often some additional assumptions. This is why it is important to characterize experimentally the dynamic of the generated states as it might improve the fidelity of the generated state.