IEEE Aerospace and Electronic Systems Magazine - November 2020 - 38

Feature Article:

DOI. No. 10.1109/MAES.2020.3004053

Opportunities and Challenges of Quantum Radar
Marco Lanzagorta, U.S. Naval Research Laboratory
Jeffrey Uhlmann, University of Missouri-Columbia

INTRODUCTION
The broad area of study referred to as quantum information science is concerned with the generalization of classical technologies to obtain improved versions that
exploit the larger class of physical properties that can be
modeled by quantum physics. In the case of computation,
this involves the generalization of physical devices capable of representing and manipulating binary states (0 or
1) to obtain devices capable of representing and manipulating a more general class of states that can only be
understood using the equations of quantum phenomena.
The topic of this article, quantum radar, is analogous in
which the goal is to generalize the states that are observable using classical radar methods so that the equations
of quantum physics can be applied to increase the
amount of available information per unit of expended
illumination energy.
The objective of this article is to describe at a high
level the fundamental elements of quantum radar and
provide insights about why it has the potential to outperform classical radar. Our goal here is not to establish
definitive statements regarding what may or may not be
practically realizable in a given timeframe, but rather
to provide a level of analysis sufficient to appreciate
why quantum radar is of interest and why there is room
for debate about its near-term prospects for practical
applications. More specifically, our analysis relies on
relatively simplistic models that are only intended to
facilitate an intuitive grasp of quantum-versus-classical
distinctions. In this regard, our analyses should be
interpreted as offering only back-of-the-envelope
evidence that quantum radar is worth of practical
consideration.
Authors' current addresses: Marco Lanzagorta, U.S. Naval
Research Laboratory, Washington, DC 20375 USA. Jeffrey
Uhlmann, Department of Electrical Engineering and Computer Science, University of Missouri-Columbia, Columbia,
MO 65211 USA (e-mail: UhlmannJ@missouri.edu).
Manuscript received July 22, 2019; accepted June 3, 2020,
and ready for publication June 22, 2020.
Review handled by Alfonso Farina.
0885-8985/20/$26.00 ß 2020 IEEE
38

The structure of the article is as follows: We begin
with a brief introduction to quantum correlations and the
extra information they potentially offer. We then provide
a general overview of how a quantum radar can exploit
this extra information. This is followed by high-level analyses of the potential advantage of quantum radar over
classical alternatives in a set of practical scenarios. We
conclude with a discussion of the theoretical and practical
issues that must be addressed in order to satisfy the
assumptions that underpin the tentative conclusions of our
analysis.

QUANTUM CORRELATIONS
The most important quantum phenomenon exploited by a
quantum radar is quantum entanglement. Let us assume
that we have two noninteracting particles A and B separated by an arbitrarily long distance. In the classical world,
the measurement of the state of A will not affect the state
of B. That is, the measurement of the state of B is independent of the measurement of the state of A. On the other
hand, in the quantum world, the measurement of the state
of A could affect the state of B. In contrast to the classical
world, the measurement of the state of B could depend on
the measurement of the state of A. When this happens, it
is said that A and B are entangled, and this is a purely
quantum property.
A more formal understanding of quantum correlations
without discussing quantum dynamics can be offered by
introducing the concept of mutual information. Information theory defines the mutual information IðA : BÞ of
two variables A and B as the amount of information
obtained about A through the measurement of B [1]. Let
us first consider a perfect classical correlation between
two binary random variables x and y. Such a correlation
can be expressed as
1
1
pðx; yÞ ¼ px dxy ¼ d00 þ d11
2
2

(1)

where dab is the Kronecker delta function. In this case, it
can be shown that the mutual information is given by
Ic ðx : yÞ ¼ 1. Thus, a perfect classical correlation has a
mutual information equal to 1.

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NOVEMBER 2020

IEEE Aerospace and Electronic Systems Magazine - November 2020

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