Taming Entangled Photons: Programmable Control of Quantum States of Light

Purdue University, West Lafayette IN

Investigators

Abstract

Taming Entangled Photons: Programmable Control of Quantum States of Light Nowhere is the strangeness of quantum mechanics more evident than in the behavior of entangled particles; measuring the state of one particle can influence that of its entangled partner, even if the pair are distantly separated. Such weird properties belie our common-sense notions of how the world works, and yet they can potentially be channeled for tremendous benefit in real-world applications. One such possibility is quantum key distribution (QKD), which relies on the laws of quantum mechanics to offer unconditional security in the transmission of information between two remote parties. In a modern world increasingly dependent on communication security, large-scale QKD represents a major goal of current research. Motivated by this objective, we are exploring new ways to manipulate and measure entangled photons based on optical pulse shaping. In a standard pulse shaper, the different frequency components of an input field are programmably manipulated to create a user-defined optical waveform at the output. By significantly extending such pulse-shaping ideas for controlling the fields involved in entangled photon experiments, we see opportunity not only to investigate new physics, but also to expand on current capabilities for imprinting and extracting information from individual light quanta, offering new possibilities for secure high-speed communications and hopefully contributing to a safer tomorrow. Specifically, we will focus on ways to use pulse shaping of classical fields for advances in (1) detection and (2) generation of entangled photons. Typically, single-photon detection is achieved with photodiodes possessing timing resolutions much longer than the duration of the photons being measured, meaning that the fine features in the temporal degree of freedom are unobservable. Accordingly, we are working to expand on a different detection scheme in which each photon is mixed with an ultrashort femtosecond pulse; then if the photon combines with the pulse through sum-frequency generation, it is possible to determine its arrival time to within the duration of the short pulse itself, permitting resolution on the femtosecond timescale and giving access to the vast information potential of frequency-time entangled photons. Our plan is to significantly expand on previous work in this area and implement an optical-fiber-compatible system for femtosecond detection, experimenting with a variety of classical fields. We will explore the possibilities for utilizing such detection in photon state characterization, demonstration of nonlocal quantum effects, and new QKD protocols. In the second major direction of this proposal, we will consider shaping of classical fields used not for detection, but rather generation of entangled photons. The spectro-temporal properties of the pump fields which produce entangled photons through downconversion can have a profound impact on the nature of the generated quantum state and "importantly for us" can be actively updated through programmable pulse shaping. In particular, we plan to consider optical frequency combs and their potential for generating new forms of entangled states, merging comb technology for optical communications with interesting quantum applications.