Continuous Variable Quantum Detector and Process Tomography.

This is the project website of the Continuous Variable Quantum Detector and Process Tomography project carried out at the Optical Quantum Technologies Group in Oxford from January 2013 to January 2015. The project was supported by the European Union through a Marie Curie Intra-European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2011-301032). Please find more information about the project below:


At the heart of all quantum technologies and fundamental tests of quantum theory lies the concept of a quantum experiment, which consists of three stages: state preparation, state evolution, and measurement. To ensure that a quantum application, such as quantum computer, is actually performing the desired task with satisfactory fidelity requires the capability to monitor each step. Quantum state and process tomography respectively prescribe procedures to completely characterize the first two stages. Tomography of quantum detectors was proposed just three years ago for discrete-variable photon-counting detection, and has yet to be developed for continuous-variable (CV) detectors such as a balanced homodyne detector (BHD). The study of CV quadrature states, processes and detection is motivated by the significantly increased complexity of such systems and the expanded capabilities that accompany this intricacy. A key advance that we propose is the complete characterization of a CV-BHD. This will be accomplished by probing the detector with known coherent states. The measurement outcomes will be analyzed using the newly developed methods of compressive sensing and operational tomography. Careful determination of BHD operation will subsequently enable us to achieve a greatly improved rendering of more involved CV quantum processes such as Fock-state filtration. By measuring the action of a process on a set of calibrated coherent states we will perform CV-quantum process tomography (QPT) of single mode processes, which are of major relevance to non-classical quantum state preparation: single photon subtraction and Fock-state filtration.


  • Michał Karpiński (researcher)
  • Brian J. Smith (supervisor)