IEEE Aerospace and Electronic Systems Magazine - November 2020 - 30

Feature Article:

DOI. No. 10.1109/MAES.2020.3004015

Evolution of Quantum Radar Concept to Noise Radar
Concept
Konstantin Lukin, IRE NAS of Ukraine; and University of Pardubice

INTRODUCTION
The quantum radar (QR) concept has been suggested in
[1] and is currently under intense investigation in both theory [2]-[5] and experiment [6]-[8]. Exploiting the unique
properties of the quantum mechanical entangled states of
a multiphoton (or multifrequency) electromagnetic (EM)
field for detection and range estimation of a distant single
target of interest is the basic idea of QR. Nowadays, the
first suggestion by authors of the patent [1] to use photon
entanglement directly, i.e., to observe changes in the idle
channel when a sounding photon hits a target, looks
impractical and will not be discussed here, though it did
provoke further investigations of the QR concept in many
research centers.
Another possible and more realistic basic approach
for QR design consists in generating two entangled photons, and using one of them as a sounding signal, while
the second one is kept in the radar as the reference (idle
signal) for its further comparison with the reflected signal, i.e., with the radar returns. Information on the target is to be extracted from estimation of covariance
matrix of the reflected signal (radar returns) and the
properly measured idle signal (reference) [6]-[8]. At the
very end of this algorithm, one has to estimate a set of
cross-correlations between in-phase and quadrature
components of the abovementioned signals. This looks
rather similar to coherent signal processing in the noise
radar (NR), where, unlike QR, classical state of photons
is used. Entanglement of photons in polarization states

Authors' current addresses: K. Lukin, LNDES, O. Ya.
Usikov Institute for Radiophysics and Electronics,
National Academy of Sciences of Ukraine, 61085 Kharkiv, Ukraine; Faculty of Electrical Engineering and Informatics, University of Pardubice, 532 10 Pardubice, Czech
Republic (e-mail: lukin.konstantin@gmail.com).
Manuscript received June 28, 2019, revised December
15, 2019, April 27, 2020, May 8, 2020; accepted May 19,
2020, and ready for publication June 18, 2020.
Review handled by Bhashyam Balaji.
0885-8985/20/$26.00 ß 2020 IEEE
30

offers another method for estimation of target parameters via detection of photon polarization changes in the
reflected signal.
There is a big hope that quantum mechanical properties of the entangled photons will enable to go beyond
classical limit in range and angular resolutions when using
entangled multiphoton radar signals [1], [2]. However, it
soon became clear that the entangled state is too fragile
and may be easily destroyed when propagating toward a
target and back because of photon losses and external
interferences affects. That is why the QR concept was
transformed into the quantum illumination (QI) concept
[3]-[6]. The main assumption of QI consists in the belief
that, in spite of destruction of the entangled state, there is
still some mutual quantum dependence called quantum
correlations. These quantum correlations may be used in
the radar measurement for estimation of the cross-correlation between idle (reference) signal and radar returns to
extract the information on the object that reflects the
sounding signal.
The above-mentioned scheme of QR is formally similar to that of NR [9]-[12], where a wideband (or narrowband) stationary random signal is used as a sounding
signal while its delayed copy serves as the reference signal
in the estimation of their cross-correlation to extract the
information on the target's range and velocity. One more
step in the evolution of the QR concept toward the NR
concept (or any coherent radar concept) has been done in
[7], where the authors stated that the signal processing
protocol in QR is the same as the one in NR, but with the
usage of quantum correlated photons as sounding and reference signals. The authors proved that one may generate
either quantum correlated photons or classical EM fields
in the same hardware. It was done via calculation of the
eigenvalues of covariance matrix composed of the measured in-phase, I, and quadrature, Q, components of the
transmitted and received signals. Expected enhancement
of QR performance with respect to that of NR (which uses
classical EM fields) has been proven for low-level signals.
However, this enhancement becomes negligible with the
increase of transmitted signal power.

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