CM – Investigation of quantum correlations of classic light sources for image transmission


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August 31, 2021

from the Chinese Academy of Sciences

There was an interesting debate about the quantum and classical origins of ghost imaging in thermal light. To clarify this quantum classical dilemma, Lixiang Chen of Xiamen University of China formulated a density matrix to fully describe the thermal two-photon orbital angular momentum state, revealing the hidden quantity with a non-zero disharmony. A teleportation mimicking scheme was then developed to demonstrate the ability to teleport an optical image with an accompanying featureless background.

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In science fiction, « teleportation » is often depicted as a means of transferring physical objects from one place to another some distance away. But in physics, quantum teleportation only transmits quantum information, i.e. the quantum state of a particle, without a physical transmission of the particle itself. The quantum protocol of teleportation was theoretically developed in 1993 by Bennett and co-workers and its first experimental demonstration was carried out in 1997 by Bouwmeester and his colleagues. towards a global scale. In the original scheme, quantum entanglement is an essential prerequisite for the implementation of teleportation.

On the other hand, ghost imaging is a fascinating imaging technique in which an image can be reconstructed using a beam of light that never touches the object interacts. However, it was shown that in addition to the quantum entangled biphoton source, classical thermal light sources can also be used to realize the task of ghost imaging, which raises the question of whether entanglement was really necessary for ghost imaging. Much excellent work has contributed, both theoretically and experimentally, but the quantum classical dilemma still lingers.

In a new article published in Light Science & Application, Lixiang Chen from the College of Physical Science and Technology of the Xiamen University, China, examines this lingering quantum classical dilemma. In a Hilbert space with photon orbital angular momentum (OAM) he formulated a density matrix in order to fully describe the two-photon state within a thermal light source, which appears as the sum of a high-dimensional OAM-entangled state and a diagonal fully separable state. Interestingly, the density matrix has been shown to be separable; H. no entanglement per se. Nevertheless, this formulation offers a physically intuitive picture to uncover the quantumness hidden in the thermal two-photon OAM state, which was characterized by a geometric discordance other than zero, which recognizes quantum correlations beyond the entanglement.

The following question naturally arises as to whether such a non-entangled but non-classical thermal two-photon state could be explored for useful quantum applications. The author answered this question positively by revisiting the quantum teleportation protocol. The numerical simulations showed that at the single photon level the thermal two-photon OAM state could be used to teleport a high-dimensional OAM state in which the retrieved state is only a mixture of an exact replica of the original state and a maximally mixed background.

In contrast to the two-dimensional polarization state, the OAM eigenstates form an infinite-dimensional, orthogonal and complete basis. Therefore, a complex amplitude optical image can be equivalently represented by a high-dimensional OAM state vector. Thus, the possibility of teleporting a clover image of both amplitude and phase modulation was also theoretically demonstrated with several iterations of the protocol.

Professor Chen summarizes the working principle of the protocol as follows: « The light field emitted by a thermal light source is split into two paths by a non-polarizing beam splitter which creates the thermal two-photon OAM state. The photon is in one path directed so that it interacts with another third photon (encoded with the complex amplitude clover image) in the high-dimensional Bell state measurement (BSM) sent in the other path to hit an ICCD camera operating in trigger mode the original image can be correctly retrieved from the ICCD camera with multiple repetitions of our protocol. « 

 » In the present proposal, the correct transmission of an image is ensured by the pure high-dimensional OAM entanglement component, while the diagonally completely mixed component merely provides a background with no marks causes.  » He added.

« Going forward, my theoretical framework may also require further studies on the use of the multiphoton thermal state to demonstrate some new quantum information tasks, such as Professor Chen’s forecasting.

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Related title :
Investigation of quantum correlations of classic light sources for image transmission
Investigation of the quantum correlation of classic light sources for image transmission


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