Entangled quantum microwaves: continuous variables for remote state preparation and quantum illumination

• Applicant: Dr. Kirill Fedorov
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2015 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275168737

• Final Report Year: 2017

Final Report Abstract

In this project, we have studied fundamental properties of propagating squeezed microwaves generated with superconducting Josephson parametric amplifiers (JPA). We have carefully investigated experimental behaviour of various JPAs and described them with analytic and numerical models. This allowed us to understand hysteretic behaviour of JPAs even for a vanishingly small screening parameter 𝛽𝐿 . Then, we have theoretically proposed and analysed several novel protocols for quantum teleportation and quantum illumination with squeezed states light in the microwave regime. We have experimentally realized and tested a fundamental displacement gate, required for universal quantum computing and communication with continuous-variable squeezed microwaves. Furthermore, we have experimentally studied finite-time correlation properties of classical and quantum states of microwave light with the help of JPAs, cross-correlation measurements, and superconducting qubits. We have demonstrated an accurate description of these experimental results with our theory models and uncovered central physical parameters governing finite-time correlations in squeezed microwave states, such as squeezing level, filter bandwidth, and noise photon number. In the end, we have applied the collected experience and knowledge to the first successful experimental implementation of the quantum communication protocol with squeezed microwaves, namely, the Remote State Preparation (RSP) protocol. This result demonstrates feasibility of quantum communication with propagating squeezed states in the microwave regime and opens the way towards more complex and applied quantum communication experiments. The latter are extremely important nowadays in the framework of recent major advances of superconducting quantum information processing. Therefore, we consider this result as an important milestone in the field of quantum communication with microwaves. With our results, we have identified several promising directions and implications for the future research. First, it became apparent that a realization of the RSP protocol with digital feedforward (feedback) is required to remotely prepare arbitrary Gaussian state, which was not possible with the current limited implementation of the analog feedforward. Alternatively, one might use two orthogonal squeezers for a full feedforward, which technically should offer the same flexibility but might be more challenging experimentally. Additionally, the digital feedforward has an advantage that it allows one for a simpler access to the classical feedback data rate, which one requires in order to experimentally assess a quantum advantage of the quantum RSP protocol over any possible classical counterpart. Second, somewhat surprising, we have observed experimental indications that the fidelity of such RSP protocols might be reliant not on quantum entanglement alone as a resource but rather on a more general class of nonclassical correlations such as quantum discord. Unique properties of quantum discord (its resistance to noise most importantly) would make this direction extremely interesting in the framework of developing novel quantum information processing protocols resistant to environmental noise. Overall, over the course of this project, we have built a basis for fundamental studies of quantum information processing with continuous-variable squeezed microwaves. Our experimental demonstration of the quantum RSP protocol highlights application opportunities of this area of physics.

Publications

• Quantum teleportation of propagating quantum microwaves, EPJ Quantum Technology 2, 25 (2015)
  R. Di Candia, K. G. Fedorov, L. Zhong, S. Felicetti, E. P. Menzel, M. Sanz, F. Deppe, A. Marx, R. Gross, and E. Solano
  
• Displacement of propagating squeezed microwaves, Phys. Rev Lett. 117, 020502 (2016)
  K. G. Fedorov, L. Zhong, S. Pogorzalek, P. Eder, M. Fischer, J. Goetz, E. Xie, F. Wulschner, K. Inomata, T. Yamamoto, Y. Nakamura, R. Di Candia, U. Las Heras, M. Sanz, E. Solano, E. P. Menzel, F. Deppe, A. Marx, and R. Gross
  
• Finite-time quantum entanglement in propagating squeezed microwaves
  K. G. Fedorov, S. Pogorzalek, U. Las Heras, M. Sanz, P. Yard, P. Eder, M. Fischer, J. Goetz, E. Xie, K. Inomata, Y. Nakamura, R. Di Candia, E. Solano, A. Marx, F. Deppe, R. Gross
  
• Hysteretic flux response and nondegenerate gain of flux-driven Josephson parametric amplifiers, Phys. Rev. Appl. (2017)
  S. Pogorzalek, K. G. Fedorov, L. Zhong, J. Goetz, F. Wulschner, M. Fischer, P. Eder, E. Xie, K. Inomata, T. Yamamoto, Y. Nakamura, A. Marx, F. Deppe, and R. Gross
  
• Photon statistics of propagating thermal microwaves, Phys. Rev. Lett. 118, 103602 (2017)
  J. Goetz, S. Pogorzalek, F. Deppe, K. G. Fedorov, P. Eder, M. Fischer, F. Wulschner, E. Xie, A. Marx, and R. Gross
  
• Quantum illumination reveals phase-shift inducing cloaking, Sci. Rep. 7, 9333 (2017)
  U. Las Heras, R. Di Candia, K. G. Fedorov, F. Deppe, M. Sanz, and E. Solano