Foundation Theoretical and Computational Physics and Astrophysics – University of Sofia (TCPA)
QuBig GmbH (QuB)
QuTools GmbH (QuT)
Université de Bourgogne (UBT)
University of Oxford (UOXF)
Background and State of the Art. Coherent interactions between light and quantum systems have attracted increasing scientific interest in optical physics. Electromagnetically induced transparency (EIT) exhibits a prominent example for such interactions. So far, EIT has been applied to control absorption and dispersion in quantum systems. The most prominent applications arise from light storage, where light pulses are converted into atomic coherences and back. This can be understood as writing and reading optical information in/from atomic coherences. TUDA is among the world leaders in EIT-based light storage, having the world record EIT storage times and storage efficiencies of light pulses and images [Phys. Rev. Lett. 111, 033601 (2013); Phys. Rev. Lett. 116, 073602 (2016)].
EIT was also proposed to enable stationary light pulses (SLPs) in ultra-dense media, i.e. light trapped in an all-optical cavity [Phys. Rev. Lett. 102, 213601 (2009)]. In contrast to light storage by EIT (where light pulses are converted into atomic coherences, i.e. “vanish” in the medium), in SLPs the light pulse “stands” in the medium without moving. SLPs permit applications in quantum information processing and related areas, e.g. to prepare entangled photons, quantum interfaces, “crystals” of photons (i.e. strongly correlated systems made of light), or novel quantum filters for single photons. The latter are a central component for any quantum technology, based on storage and operation of single photons.
The industry teams QuT and QuB will contribute to the experimental and technological investigations at the academic partners TUDA, UoS and UOXF by know-how transfer and development of specific enabling optical technologies. These include efficient single-photon detectors, ultra-fast electronic modules and appropriate software to process single-photon data made by QuT, as well as fast electro-optical devices made by QuB to shape the temporal profile of the driving laser pulses. These technologies are absolutely crucial for any experiment in quantum optics, e.g. in the regime of few or single photons – as relevant for the experiments at TUDA, UoS and UOXF. In turn, the successful implementation of quantum technologies is expected to open a new, future market for novel quantum devices as well as the required enabling technologies. Thus, the academia / industry cooperation exhibits a “win-win situation” for both sides with the potential of long-term contacts of commercial relevance.
In related projects towards optical devices for quantum information processing, partner UBT has studied novel coherent propagation effects involving classical light with particular focus on information storage and transfer, control of the pulse propagation and shaping. The control of the speed of light (for both transmission and reflection) in the medium is an important topic for investigation. A technique has been shown in the joint analysis by TUDA and UBT in lambda three-level system via STIRAP-type processes [Phys. Rev. A 80, 033402 (2009)]. Moreover, UBT has developed an adiabatic Floquet theory that allows the control of the exchange of photons between two (laser or quantized) fields coupled to mediating atoms [Phys. Rev. A 63, 031403(R) (2001)]. This tool will be extended when phonon modes (of a trap) are additionally taken into account, and also considered to produce complex photonic wavepackets by robust techniques, for instance from a leaking cavity in connection with WP2.
We will implement techniques to manipulate light (in particular single-photon or a few photon wavepacket) by light (i.e. control laser pulse), e.g. aiming at novel techniques to store, shape and process photons as carriers of optical information bits. The work is strongly connected to WP 1 (robust methods and non- linear quantum systems) and to WP 2 through shared interests in photon manipulation, quantum networking and enabling technologies. Four ESRs are mainly assigned to WP 3. The particular aim is to implement quantum nonlinear optics using SLPs in an ultra-cold atomic medium at high optical depth. This will, e.g., allow for the creation of a quantum filter for single photons, i.e. a central element of a light source for quantum technologies. We will also develop optical tools for quantum technology such as microscopes or spectrometers allowing time-resolved single photon detection and high timing resolution (QuT) and a universal electro-optic modulator (QuB).