RQC Seminar

158th RQC Seminar

• Speaker

  Mr. Francesco Anna Mele
  ( Scuola Normale Superiore di Pisa )

• Date

  14:00-15:00, September 18, 2024 (Wednesday)

• Venue

  Onsite( Wako Main Research Bldg. 3F 345-347 Seminar Room/ 研究本館3階 セミナー室(345-347) C01）

• Title

  Learning quantum states of continuous variable systems

• Inquiries

  rqc_info[at]ml.riken.jp

Abstract
Quantum state tomography, aimed at deriving a classical description of an unknown state from measurement data, is a fundamental task in quantum physics. In this work, we analyse the ultimate achievable performance of tomography of continuous-variable systems, such as bosonic and quantum optical systems. We prove that tomography of these systems is extremely inefficient in terms of time resources, much more so than tomography of finite-dimensional systems: the minimum number of state copies needed for tomography not only scales exponentially with the number of modes but also exhibits a dramatic scaling with the trace-distance error, even for low-energy states, in stark contrast with the finite-dimensional case. On a more positive note, we prove that tomography of Gaussian states is efficient. To accomplish this, we answer a fundamental question for the field of continuous-variable quantum information: if we know with a certain error the first and second moments of an unknown Gaussian state, what is the resulting trace-distance error that we make on the state? Lastly, we demonstrate that tomography of non-Gaussian states prepared through Gaussian unitaries and a few local non-Gaussian evolutions is efficient and experimentally feasible.