The process of heralded noiseless amplification, and the inverse process of
heralded noiseless attenuation, have potential applications in the context of
quantum communications. Although several different physical implementations of
heralded noiseless amplifiers have now been demonstrated, the research on
heralded noiseless attenuators has been largely confined to a beam-splitter
based approach. Here we show that an optical parametric amplifier (OPA),
combined with appropriate heralding, can also serve as a heralded noiseless
attenuator. The counterintuitive use of an optical amplifier as an attenuator
is only possible due to the probabilistic nature of the device.Comment: 3 pages, 1 figur
We consider a coherent state of light propagating through an ensemble of two-level atoms where all the atoms are initially in their ground state. In ordinary absorption, the transition of atoms to their excited state along with the absorption of a photon will remove energy from the beam and attenuate the signal. Here we show that post-selecting on those cases in which none of the atoms made a transition to the excited state can give even more attenuation than would normally occur due to absorption. The same process can also produce amplification when there is a sufficiently strong interaction between the photons and the atoms.
The quantum Zeno effect reveals that continuous observation of a quantum system can significantly alter its evolution. Here, we present a method for establishing polarization entanglement between two initially unentangled photons in coupled waveguides via the quantum Zeno effect. We support our analytical investigation with numerical simulations of the underlying Schrodinger equation describing the system. Further, we extend our technique to three coupled waveguides in a planar configuration and determine the parameters required to generate three-qubit W-states. In contrast to existing schemes based on a vacuum and single-photon encoding, the polarization encoding in our approach is compatible with quantum information protocols that remove photon loss through post-selection. Our findings offer a powerful quantum state engineering approach for photonic quantum information technologies.
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