Controlling Light with Photon Subtraction via the Single-Photon Raman Interaction

Abstract

This dissertation leverages deterministic photon subtraction based on the single-photon Raman interaction (SPRINT) to engineer multiphoton quantum fields and design quantum optical platforms for applications ranging from non-Gaussian quantum light generation to photon-number-resolving (PNR) detection and photon number splitting (PNS) attacks on quantum key distribution (QKD). The work is structured into four main parts.

In the first part (Chapter 2), we evaluate the performance of the subtraction scheme using system parameters that are technologically accessible according to the current state of the art. We analyze the photon subtraction process in a configuration where the transitions of a Λ-type emitter are selectively coupled to the stationary modes of a bimodal cavity, which are in turn coupled to distinct waveguide modes. Using the input-output formalism of quantum optics and quantum trajectory methods, we investigate single- and multiphoton transport in the system. The results indicate that success rates approaching unity are achievable with currently reported coupling rates for cold atoms trapped in crossed optical-fiber cavities as well as for solid-state platforms based on quantum dots.

In the second part (Chapter 3), we explore the capability of the photon subtraction scheme to generate non-Gaussianity in initially Gaussian input fields. Using a photon subtractor with the emitter directly coupled to a chiral waveguide, we show that for both squeezed vacuum and coherent light input pulses, the Wigner function of the output field clearly reveals its non-Gaussian character following photon subtraction. Furthermore, we propose a measurement-based scheme on the subtracted photon which can lead to conditional generation of quantum states resembling Schrodinger’s kitten state directly from coherent input light with fidelities above 99%. This result is particularly noteworthy, as coherent pulses, unlike the squeezed vacuum inputs commonly used in previous studies, are readily available experimentally.

The last two parts of the dissertation explore the possibilities arising from cascading multiple photon subtractors. In the third part (Chapter 4), we investigate the operation of a PNR detector composed of a cascade of waveguide-coupled Λ-type emitters, which deterministically demultiplexes incoming photons among single-photon detectors. We present a closed-form expression for the detector’s precision in the linear regime and predict how correlations generated by nonlinear photon-photon interactions influence this precision. We compare the performance of the proposed PNR detector with that of a conventional PNR scheme based on spatial demultiplexing via beamsplitters. Our results indicate that the proposed scheme can outperform conventional detectors under realistic conditions, making it a promising candidate for next-generation PNR detection.

In the fourth part (Chapter 5), we present a specialized photon subtraction scheme that enables the deterministic extraction of single photons from multiphoton states while leaving input single-photon states unaltered. The proposed device consists of a two-way cascade of two Λ-type emitters coupled via a chiral waveguide. We analyze the interaction of this system with traveling few-photon pulses of coherent light and use these results to highlight how this two-emitter extension improves the original deterministic single-photon subtraction when it comes to implementing undetectable PNS attack on a QKD channel. Finally, in Chapter 6, we demonstrate how this two-emitter approach can be extended to an n-emitter cascade, resulting in a photon subtractor that selectively extracts photons from an input light stream based on their arrival time sequence. We show that this photon subtractor enables the generation of high-fidelity and modal purity multiphoton Fock states. The application of these Fock-state pulses in optical interferometry is investigated, highlighting their potential for quantum metrology at the Heisenberg limit. These results introduce novel applications of SPRINT-based photon subtraction in areas ranging from non-Gaussian photonics, to PNR detection, QKD, and quantum metrology.