In entanglement assisted communications and sensing the optical phase-conjugation (OPC), required before homodyne detection takes place, is typically performed on signal photons on receive side. Unfortunately, in turbulent free-space optical channels, the signal photons can be scattered or absorbed by the channel, and if they reach the receive side they are very weak. Here we propose an entanglement assisted radar technique in which the OPC is performed on bright idler photons instead. By performing the OPC on idler photons on transmit side, while employing adaptive optics and classical homodyne detection on receive side, we experimentally demonstrate that the target detection probability of the proposed entanglement assisted radar over turbulent free-space optical channel is significantly better than that of corresponding classical detection scheme.
In entanglement assisted communications and sensing the optical phase-conjugation (OPC), required before homodyne detection takes place, is typically performed on signal photons on receive side. Unfortunately, in turbulent free-space optical channels, the signal photons can be scattered or absorbed by the channel, and if they reach the receive side they are very weak. Here we propose an entanglement assisted radar technique in which the OPC is performed on bright idler photons instead. By performing the OPC on idler photons on transmit side, while employing adaptive optics and classical homodyne detection on receive side, we experimentally demonstrate that the target detection probability of the proposed entanglement assisted radar over turbulent free-space optical channel is significantly better than that of corresponding classical detection scheme.
In this invited paper we review our recent research activities on experimental demonstration of entanglement based (EB) radars, operated over strong atmospheric turbulence channels. In conventional EB communications, sensing, and radars the phase-conjugation, required before homodyne detection takes place, is performed on received signal photons. In atmospheric turbulent channels, the signal photons are affected by diffraction, absorption, scattering, and atmospheric turbulence effects so that only limited number of weak target probe returned signal photons reach the receiver side in EB radars. Moreover, it is extremely difficult to perform any phase-conjugation on weak signal photons when the average number of received photons is <<1. To solve this problem, we have recently proposed to perform phase-conjugation on bright idler photons instead. Namely, we perform the wavelength conversion by the PPLN waveguide on bright idler photons, so that the idler photons will have the same wavelength as the signal photons, and after that we use a classical homodyne balanced detector as an entanglement assisted detector. To generate entangled photon pairs, we use C-/L-band tunable laser, EDFA, the PPLN waveguide, and WDM demultiplexers. To demonstrate the high-potential of the proposed EB radar concept, we developed an experimental outdoor free-space optical (FSO) testbed at the University of Arizona campus. Using this FSO testbed we experimentally demonstrate that the proposed EB radar significantly outperforms the corresponding classical counterpart and can operate in strong turbulence regime. To improve the detection probabilities further, we use deformable mirror-based adaptive optics.
Entanglement based (EB) communication, networking, and sensing represent excellent alternatives to corresponding classical counterparts in particular in either lowbrightness or high-attenuation regime and when the signal photons are buried in noise. In EB applications idler photons are stored in memory while the signal photons, carrying information, are transmitted over lossy, noisy, and for communication/networking over free-space optical (FSO) channels signal photons are also affected by the atmospheric turbulence and scattering effects. In optical phase conjugation (OPC)-based EB receiver, the OPC operation is performed on signal photons, which are severely affected by FSO channel impairments, with many signal photons being either absorbed or scattered by the FSO channel. Here we propose to perform the OPC operation on idler photons instead. The OPC operation is performed using low-cost, C-band components including tunable laser, periodically polled lithium niobate (PPLN) waveguides, tunable filter, and WDM demultiplexer; and this implementation is suitable for the photonic integrated circuit (PIC) realization. A similar approach is applied to implement the C-band devicesbased entanglement source. Given that the idler photons are brighter compared to the signal photons transmitted over either FSO channel or fiber-optics channel, the OPC operation is much more efficient. In the OPC-based receiver for FSO communications, we need to couple the signal photons to the single-mode fiber (SMF) before the OPC takes place, making the OPC process sensitive to the FSO-to-SMF coupling inefficiency. By performing the OPC on the idler photons instead, the OPC process is insensitive to poor coupling efficiency. In addition to being superior in terms of spectral efficiency compared to classical counterparts, in particular in highly lossy and noisy environment, the proposed EB scheme with the phaseconjugation on idler photons is superior to the corresponding scheme performing the phase-conjugation on signal photons in terms of receiver sensitivity making it an attractive option for radar applications. To validate the proposed concept at the University of Arizona campus we have developed a terrestrial FSO testbed. For detection probability of 0.99 the proposed EB radar outperforms the classical counterpart by 6.7 dB. We experimentally demonstrate that the target detection probability of the proposed entanglement based radar over turbulent FSO channel is significantly better than that of corresponding classical detection scheme.
Entanglement is a unique quantum information processing feature. With the help of entanglement we can build quantum sensors whose sensitivity is better than that of classical sensors. In this paper we are concerned with the entanglement assisted (EA) bistatic quantum radar applications. By employing the optical phase conjugation (OPC) on transmitter side and classical coherent detection on receiver side we show that the detection probability of the proposed EA target detection scheme is significantly better than that of corresponding classical and coherent states-based quantum detection schemes. The proposed EA target detection scheme is evaluated by modelling the radar return channel as the lossy and noisy Bosonic channel and assuming imperfect distribution of entanglement over the idler channel.
Optical communications over terrestrial free-space optical (FSO) channels are affected by various effects including diffraction, absorption, scattering, and turbulence effects. In several recent papers we have shown that entanglement assisted (EA) communication systems significantly outperform corresponding classical counterparts in strong turbulence regime. In traditional EA communications the phase-conjugation, required before the homodyne detection takes place, is performed on signal photons. However, given that many photons get lost due to diffraction, scattering, absorption, and turbulence effects, it is extremely difficult to perform the phase-conjugation on received signal photons when average number of received photons is smaller than 1. To solve this problem, we recently have proposed to perform phase-conjugation on bright idler photons instead. To operate the EA communication system over turbulent FSO links it is required to generate many bright entangled photons so that signal photons can survive beyond strong turbulence regime. To solve this problem, we have proposed to properly design periodically poled lithium niobate waveguides so that we can use telecom available lasers operated in S-, C-, and L-bands as the pump lasers instead of high-cost 780 nm pump lasers. In this invited paper, we will review our recent activities in EA communion studies over terrestrial FSO links and present recent experimental results demonstrating that EA communication systems performing the phase-conjugation on idler photons significantly outperforms both classical counterpart and the EA communications with phase-conjugated receiver in strong turbulence regime.
In this invited paper, we describe our entanglement assisted (EA) MIMO quantum radar technique with multiple entangled transmitters and coherent detection-based receivers. This scheme exploits the phase sensitive quantum correlation on the receivers’ sides to improve the receiver sensitivity. To increase overall signal-to-noise ratio, we use the spatial MIMO concept. To reduce the system cost and complexity, the optical phase conjugation (OPC) on signal photons is performed on a transmitter side, so that commercially available classical, balanced coherent detectors can be used on receiver side instead of traditional OPC-based EA receivers.