Two current hurdles of quantum RADAR/LiDAR technology are i.) The use of joint measurement techniques, whereby the idler remains in a delay line or a quantum memory to be measured later with the returning signal, and ii.) The difficulty in creating high photon flux signals for long range sensing. Our measurement and detection protocol using immediate-idler-detection (IID) helps to alleviate both of these issues. We present our recent experimental data from characterizing our proof-of-concept IID quantum LiDAR system and show that similar to delay line approaches, we achieve strong correlation even in extremely noisy channels where the noise level exceeds the signal strength by as much as one hundred times. We have found that even in very lossy channels, the integration time remains extremely short and roughly the same value even as the noise is increased. We also show preliminary results through foggy free space channels and found positive correlation SNR even when the visibility was as low as 15%. Our measurement and detection protocol was designed to align closely with classical RADAR and LiDAR signal processing to better align the quantum and classical sensor regimes and allows for the potential to scale upwards and produce higher photon-flux signals from multiple photon pair sources.
Modern approaches to quantum radar implementation utilize the intrinsic correlations of two-mode squeezed vacuum photon pairs emerging from a nonlinear interaction. The most popular approach has been the use of delay lines for the idler and performing joint measurements on the idler and returning signal together. In this paper, it is argued and shown that this sort of implementation is not necessary to extract the quantum cross correlation terms. Immediate detection of the idler and later cross correlation on a large enough data set will yield identical covariance terms. Moreover, immediate idler detection facilitates the use of conventional radar signal processing which allows existing waveform toolboxes of classical radar to be utilized for quantum radar. This allows a much more relaxed set of constraints on the implementation of quantum radar techniques. This paper discusses these concepts, including new detection techniques from the author, and validates the framework with some preliminary experimental data. The presented data, as well as the recent work of others allows for the possibility of a much larger quantum advantage than previously thought, particularly when comparing to real-world practical classical sensors.
KEYWORDS: Quantum key distribution, Time correlated photon counting, Error control coding, Quantum entanglement, Data transmission, Photon counting, Digital watermarking, Quantum information
We introduce a novel QKD protocol which utilizes the intrinsic temporal correlations found in photon pairs from a two-mode squeezed vacuum (TMSV) state. Upon generation, the idler photons are measured right away by Alice, and their time stamps recorded. This idler detection heralds the corresponding signal photons traveling in the channel towards Bob, which ensures the temporal configuration of the photons is identical between the two sets of photons when Bob measures them as a later time. By converting the time intervals between these photons into an uniformly-distributed integer stream, we generate two matching streams of integers which can be used to generate a secure key. The security of this key-generation scheme is discussed and investigated, as well as the utilization of this system in a real-world environment. The introduction of dropped photons and dark counts requires the use of non-standard error correcting codes. We discuss the use of Marker codes in the system and how correction and privacy amplification can occur without allowing knowledge of the full key to transmit to an eavesdropper.
In recent years, quantum radar has focused entirely on using bipartite squeezed states of light as a mechanism for target detection. This paper studies the performance of a quantum radar that uses a tripartite squeezed state, whereby two signal beams are sent out towards the target which both correlate with the idler. It is found that for very low signal strengths, the bipartite has better performance. As the signal strength increases however, the tripartite becomes dominant. This result suggests that quantum radar (declared useful only in the low SNR regime) may possess more possibilities of increased performance at higher SNRs when different states are used for correlation. The bottleneck, of course, is the ability to generate transmit powers necessary to utilize.
KEYWORDS: Single photon, Binary data, Signal to noise ratio, Modulation, Sensors, Radar, Computer simulations, Signal detection, Monte Carlo methods, Entangled states
Recently, much of the quantum radar/lidar research is focused on correlating single photon detection events with no delay line on the idler path. In other words, measuring the idler immediately, and correlating these events with later received photon events from the returning signal. This research approach has raised some questions due to the fact that all measurements done are classical, yet researchers are still observing sensor improvement in comparison to classical techniques. This therefore implies that the benefits from quantum radar/lidar using these techniques should be able to be explained entirely classically. This paper explores this concept by asserting that the correlation between the signals used in quantum remote sensing is largely due to the fact that the signal and idler photons are created simultaneously (which is only possible from an entangled source). We show, using very simple computer simulations, that having a single photon correlated (binary) waveform leads to correlation SNR advantages only in the low photon level regime, agreeing with previous literature.
KEYWORDS: Radar, Beam splitters, Single photon, Remote sensing, Signal to noise ratio, Photon counting, Analog electronics, Interference (communication), Matrices, Applied research
In this paper, we derive the electric field covariance matrix of the signal and idler beams from an entangled source for applications involving quantum radar. We also derive the corresponding covariance matrix for a classical matched filtering remote sensing system and compare to the quantum result. We use this comparison to derive an expression for the quantum enhancement factor as a function of the mean photon number per mode, Ns. This result is significant because it allows one to exactly calculate the predicted quantum enhancement as a function of transmit power, rather than only having an upper bound. Additionally, we look into previous analog correlation techniques using an optical parametric amplifier (OPA) and show that immediately detecting the idler produces the same cross correlation terms. However, the actual measurements needed to harness these correlations is enhanced when one immediately detects the idler because it minimizes the added noise caused by the additional length of the idler path in the conventional method. Finally, our results also show that one does not need to count photons to harness these correlations, but rather, perform electric field measurements.
Within the last decade, the field of quantum remote sensing has garnered a lot of interest from the radar and communication community. Many papers on this topic have compared the performance of a classical system versus a quantum system. However, the concept of a system using both classical and quantum components in conjunction has not been explored thoroughly. This paper documents the design and simulation of a quantum + classical cooperative remote sensing design in the optical regime. The arrangement uses quantum correlations created by entangled photons in addition to conventional classical waveform correlations. We show that the composite quantum + classical system exhibits increased performance compared to a pure classical system alone.
In this paper, we discuss the effect that photon polarization has on the quantum radar cross section (QRCS) during the special case scenario of when the target is enveloped in either a uniform electric field or magnetic field and all of its atomic electric/magnetic dipole moments become aligned (target polarization). This target polarization causes the coupling between the photon and the matter to change and alter the scattering characteristics of the target. Most notably, it causes scattering to be very near zero at a specified angle. We also investigate the relationship between electric and magnetic types of coupling and find that the electric contribution dominates the QRCS response.
The effectiveness of various dynamic calibration targets emulating human respiration are analyzed. Potential advantages of these devices relate to easier calibration methods for human detection testing in through-wall and through-rubbles situations. The three devices examined possess spherical polyhedral geometries. Spherical characteristics were implemented due to the unique qualities spheres possess in regards to calibration purposes. The ability to use a device that is aspect independent is favorable during the calibration process. Rather than using a traditional, static calibration sphere, a dynamic, sphere-like device offers the ability to resemble breathing movements of the human body. This motion opens the door for numerous types of Doppler testing that is impossible in a static calibration device. Monostatic RCS simulations at 3 GHz are documented for each geometry. The results provide a visual way of representing the effectiveness of each design as a dynamic calibration target for human detection purposes.
It has been found that the quantum radar cross section (QRCS) equation can be written in terms of the Fourier transform of the surface atom distribution of the object. This paper uses this form to provide an analytical formulation of the quantum radar cross section by deriving closed form expressions for various geometries. These expressions are compared to the classical radar cross section (RCS) expressions and the quantum advantages are discerned from the differences in the equations. Multiphoton illumination is also briefly discussed.
Quantum radar is an emerging field that shows a lot of promise in providing significantly improved resolution compared to its classical radar counterpart. The key to this kind of resolution lies in the correlations created from the entanglement of the photons being used. Currently, the technology available only supports quantum radar implementation and validation in the optical regime, as opposed to the microwave regime, because microwave photons have very low energy compared to optical photons. Furthermore, there currently do not exist practical single photon detectors and generators in the microwave spectrum. Viable applications in the optical regime include deep sea target detection and high resolution detection in space. In this paper, we propose a conceptual architecture of a quantum radar which uses entangled optical photons based on Spontaneous Parametric Down Conversion (SPDC) methods. After the entangled photons are created and emerge from the crystal, the idler photon is detected very shortly thereafter. At the same time, the signal photon is sent out towards the target and upon its reflection will impinge on the detector of the radar. From these two measurements, correlation data processing is done to obtain the distance of the target away from the radar. Various simulations are then shown to display the resolution that is possible.
Quantum radar serves to drastically improve the resolution of current radar technology using quantum phenomena. This paper will first review some of the proposed ideas and engineering designs behind both entanglement radar and coherent state radar design schemes. Entanglement radar is based on first entangling two photons, then sending one of the entangled photons out towards the target, and keeping the other one at home. A correlation between the two photons is analyzed to obtain information. Coherent state quantum radar relies on using coherent state photons and a quantum detection scheme in order to beat the diffraction limit. Based on the above, a proposed design concept to implement of a coherent state quantum radar is presented for simultaneously determining target range and azimuth/elevation angles.
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