Characterizing frequency correlations via polarization measurements : Using the decoherence of a two-photon polarization state as a tool to measure frequency correlations in spontaneous parametric down conversion
Moreno, Jaime (2023)
Moreno, Jaime
2023
Master's Programme in Photonics Technologies
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-11-14
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202310259100
https://urn.fi/URN:NBN:fi:tuni-202310259100
Tiivistelmä
Developing techniques for characterizing quantum mechanical systems has been a major topic of research, especially in recent years, as quantum technologies, such as quantum communication and quantum cryptography, have grown to become an important asset in modern society. Although techniques such as quantum state tomography is an effective method to characterize a system consisting of two-level systems, the characterization of continuous degree of freedom such as space or frequency stills represents a time-consuming task as the state space scales exponentially with the dimension of the system. In this work, we show an indirect approach for measuring properties of high-dimensional degrees of freedom by coupling them to two-dimensional subsystems that can be measured efficiently via quantum state tomography. In our case, the property of interest is the correlation factor of the joint spectral amplitude describing the two-photon frequency states, which are coupled to the polarization degree of freedom using a completely positive trace-preserving map, called a dephasing channel. The action of the map on the polarization state induces a decoherence effect that depends on the initial frequency state, thus allowing to retrieve information about the frequency correlation factor by only measuring the decoherence in the polarization state.
In the experimental part, we produced a pair of photons using spontaneous parametric down-conversion and characterized the joint spectral intensity with stimulated emission tomography. The decoherence was controlled with a birefringent material that acts as a dephasing channel. The polarization state was measured after the dephasing channel for two different initial frequency configurations using quantum state tomography. The bounds for the frequency correlation factor were calculated from the fidelity of the two polarization states and the generalized data processing inequality. The results of this work show that the polarization decoherence can be used as a tool to measure the frequency correlation factor of the joint spectral amplitude.
In the experimental part, we produced a pair of photons using spontaneous parametric down-conversion and characterized the joint spectral intensity with stimulated emission tomography. The decoherence was controlled with a birefringent material that acts as a dephasing channel. The polarization state was measured after the dephasing channel for two different initial frequency configurations using quantum state tomography. The bounds for the frequency correlation factor were calculated from the fidelity of the two polarization states and the generalized data processing inequality. The results of this work show that the polarization decoherence can be used as a tool to measure the frequency correlation factor of the joint spectral amplitude.