## Research

Some topics that fascinate us are listed here:

### Interfacing quantum and biological systems

What does it take to detect the quantum nature of a given state? Can a biological sensor — with its many imperfections — detect entanglement? We are working along these lines with the aim to lay the basis for a new class of experiments interfacing quantum and biological detectors. For example, the Templeton Foundation is supporting us in order to develop the first experiment where entanglement is revealed with the human eye.

- Proposal for witnessing non-classical light with the human eye
- What does it take to detect entanglement with the human eye?
- Seeing quantum superpositions

### Quantum Networks

The distribution of quantum states over long distances has important applications, for example, in quantum key distribution.
However, this distribution is inherently limited by photon loss, and direct amplification as used in classical telecommunication is not an option in quantum communication due to the no-cloning theorem.
This could be overcome with the use of quantum networks. We work hand in hand with leading experimental groups on each component of these networks. This includes protocols for entanglement creation and entanglement purification, quantum memories and network certification. SCINET is one example of an ongoing project that clearly illustrates what we do in the framework of quantum networks.

- Quantum repeaters based on atomic ensembles and linear optics
- Quantum storage of photonic entanglement in a crystal
- Prospective applications of optical quantum memories

### Macroscopic Quantumness

Defining and quantifying macroscopicness in quantum theory is one of our objectives. We intend to establish a complete mathematical framework to measure and compare the size of quantum states describing either photonic, atomic or mechanical systems. Progress along these lines might allow us to challenge old yet unsolved problems, for example, related to the transition from the quantum to classical world. Beside their fundamental interest, the extreme sensitivity of macroscopic quantum states make them appealing for applied physics. We are interested in their application in quantum sensing and metrology.

- Displacement of photonic quantum states towards the macroscopic domain
- Proposals for optomechanical sensing of collapse models
- How difficult is it to prove the quantumness of macroscopic states?

### Device Independent Certification

How can one extend a random bit string in a trustworthy manner? How can we guarantee the secrecy of a quantum key with minimal assumptions about the device used to produce the key? Are we able to certify the quantumness of a many-body state without knowing the dimension of the underlying Hilbert space nor the internal working of the device used to measure it? Bell tests, which were initially proposed to detect non-local correlations, provide unique conceptual tools for answering these questions. We are working in close collaboration with several experimental groups to bring device-independent quantum information processing closer to practical implementation.