Abstract
Decoherence remains one of the most serious challenges to the implementation of quantum technology. It appears as a result of the transformation over time of a quantum superposition state into a classical mixture due to the quantum system interacting with the environment. Since quantum systems are never completely isolated from their environment, decoherence therefore cannot be avoided in realistic situations. Decoherence has been extensively studied, mostly theoretically, because it has many important implications in quantum technology, such as in the fields of quantum information processing, quantum communication and quantum computation. Here we report a novel experimental scheme on the study of decoherence of a two-mode squeezed vacuum state via its second harmonic generation signal. Our scheme can directly extract the decoherence of the phase-sensitive quantum correlation $\langle \hat{a}\hat{b}\rangle$ between two entangled modes $a$ and $b$. Such a correlation is the most important characteristic of a two-mode squeezed state. More importantly, this is an experimental study on the decoherence effect of a squeezed vacuum state, which has been rarely investigated.
Highlights
Realistic quantum systems are inevitably coupled with their environment
There are some experimental investigations using decoherence for testing quantum mechanics [33]. These experiments are useful for evaluating the predictions of decoherence models and offering guidance for designing quantum devices that are capable of circumventing the detrimental influence of the environment. Among these prior experimental studies on decoherence, some are of particular interest to us due to the fact that they were conducted in an “all-optical” manner; for instance, Kwiat et al used polarization-entangled photon pairs produced by spontaneous parametric down-conversion (SPDC) to search for decoherence-free subspaces [15]
The finite length of the atomic vapor cell (12.5 mm) slightly relaxes the longitudinal phase-matching condition and allows for a range of angles, which effectively sets the angular acceptance of the four-wave mixing (FWM) process and produces the two-mode squeezed vacuum (TMSV) state in a form of “light cone” after the cell
Summary
Realistic quantum systems are inevitably coupled with their environment. When a quantum system interacts with its environment, it will in general become entangled with a large number of environmental degrees of freedom [1,2,3,4,5,6,7,8]. These experiments are useful for evaluating the predictions of decoherence models and offering guidance for designing quantum devices that are capable of circumventing the detrimental influence of the environment Among these prior experimental studies on decoherence, some are of particular interest to us due to the fact that they were conducted in an “all-optical” manner; for instance, Kwiat et al used polarization-entangled photon pairs produced by spontaneous parametric down-conversion (SPDC) to search for decoherence-free subspaces [15]. Since direct measurement schemes such as intensity detections are not able to extract information about quantum correlation ab , they can only extract information about correlation a†ab†b ; our experimental scheme is set up in such a way that through the SHG signal induced by entangled photon pairs, information about the decoherence of the quantum correlation abcan be extracted explicitly
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