Abstract
One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution.
Highlights
For a high gain phase insensitive optical parametric amplifier, there are two output ports with nearly identical powers11–14
To produce an input test signal for the amplifier, the combined signal beam is encoded by phase modulation (PM) with an electro-optic modulator (EOM)
Since the noise level of FOPA2 is sensitive to the phase difference of the pumps P1 and P2 (see Eq [6]), we control the phase of P2 by mounting a piezo-electric transducer (PZT) on a high reflection mirror
Summary
For a high gain phase insensitive optical parametric amplifier, there are two output ports with nearly identical powers. After passing through a sample for information coding, the bright encoded probe and the spontaneous idler field are input to FOPA2 at the signal and idler input ports, respectively. In this way, the noise of the input signal is correlated with the amplifier’s internal mode. For the purpose of encoding information, we will need to have a beam with non-zero coherent part propagate through a test sample We achieve this by combining a bright coherent state |α/t〉with one (signal) of the entangled fields generated from FOPA1 in a beam splitter (BS) with amplitude transmittance t. The signal level for the input of FOPA2, which carries the information of the sample, has a non-zero coherent part of |α〉
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