Quantum Optics Theory

The modern capacity to engineer, control, and measure correlated quantum states using quantum fields and optical elements is the basis for our interest to explore how to implement quantum information, communication, and computation protocols and investigate fundamental aspects of quantum mechanics in the quantum-optical setting. We are interested in understanding quantum-correlated fields and the quantum theory of measurements for further understanding of the fundamental behavior of nature as well as their applications for quantum technologies that promise novel applications beyond those achievable with classical resources.

The latest works of our group in this direction are related to the characterization of dissimilar notions of quantum correlations that have been established and the proposal of experimentally accessible certification criteria. Such topics bring us close to questions explored by experimental physicists, mathematicians, and information scientists. Hence, our multiple and fruitful collaborations on the topic. Such different kinds of quantum effects have been motivated through particular applications in quantum information science. In particular, we rigorously defined different notions of entanglement in the context of first and second quantization [1]. An observation that not only affects our fundamental understanding but has direct implications on quantum technology which can harness those different forms of entanglement in practical scenarios. We also have devised a method to certify nonclassical features via correlations of phase-space distributions by unifying the notions of quasiprobabilities and matrices of correlation functions [2]. Such a method was implemented experimentally [3] based on the reconstructed Wigner and Husimi Q functions, our inequality conditions detect nonclassicality despite the fact that the involved distributions are nonnegative, which includes cases of high loss and cases where other established methods do not reveal nonclassicality. We also collaborated on the experimental realization of a form of quantum correlation that exists even in the absence of entanglement and discord, and we theoretically show how multimode entanglement can be activated based on the generated, unentangled state [4]. The fast and accessible verification of nonclassical resources is an indispensable step towards a broad utilization of continuous-variable quantum technologies. We have used machine learning methods for the identification of nonclassicality of quantum states of light by processing experimental data obtained via homodyne detection [5].


  1. Jan Sperling and Elizabeth Agudelo, Entanglement of particles versus entanglement of fields: independent quantum resources, arXiv:2204.06245 [quant-ph] (2022).
  2. Martin Bohmann, Elizabeth Agudelo, Jan Sperling, Probing nonclassicality with matrices of phase-space distributions, Quantum 4, 343 (2020) [arXiv: 2003.11031].
  3. Nicola Biagi, Martin Bohmann, Elizabeth Agudelo, Marco Bellini, and Alessandro Zavatta, Experimental Certification of Nonclassicality via Phase-Space Inequalities, Phys. Rev. Lett. 126, 023605 (2021) [arXiv:2010.00259].
  4. S. Köhnke, Elizabeth Agudelo, M. Schünemann, O. Schlettwein, W. Vogel, J. Sperling, and B. Hage, Quantum Correlations beyond Entanglement and DiscordPhys. Rev. Lett. 126, 170404 (2021) [arXiv:2010.03490].
  5. Valentin Gebhart, Martin Bohmann, Karsten Weiher, Nicola Biagi, Alessandro Zavatta, Marco Bellini, and Elizabeth Agudelo, Identifying nonclassicality from experimental data using artificial neural networks, Phys. Rev. Research 3, 023229 (2021) [arXiv:2101.07112].