one + one is not two
TRANSCRIPT
-
7/28/2019 One + One is Not Two
1/4
Vol. 10 | Spring 2013 www.onr.navy.mil/innovate
1
INNOVATIONOffice Of Naval ReseaRch vOl. 10 | spRiNg 2013
-
7/28/2019 One + One is Not Two
2/4
www.onr.navy.mil/innovate Vol. 10 | Spring 2013
8
shared private keys that appears immune
to eavesdropping. It has been commercially
available for several years now. In the
Informac Phenomena Group at Naval Research
Laboratory (NRL), our view on QIS is thattechnologies like quantum key distribuon
represent a small fracon of the areas true
potenal. Our posion is not merely intended
to help safeguard against overinvestment. It is
also grounded in the belief that within the realm
of Informaon Technology, changing the basic
unit of informaon from classical to quantum
could be a 21st century version of spling the
atom. Only when the central idea in QIS is taken
seriously, that it is an enrely new paradigm
of informaon, and only when we learn how
to naturally apply its laws, do we expect to see
it have a revoluonary and lasng impact on
Informaon Technology.
At the center of this new paradigm lies the
qubit: a revoluonary challenge to the classical
bit. A classical bit can assume either the value
0 or 1. A quantum bit, or qubit, is capable of
being 0, 1 or anything in between 0 and 1.
Unlike classical bits, qubits cannot necessarily
+ is noTInnovaon is somemes the result of
re-examining certain fundamental beliefs about
the way the world works. To illustrate, consider
a few of the simple quesons one can ask about
informaon:
(a.) Can informaon always be copied?
(b.) Given two idencal pieces of
informaon, can we read each one and
get dierent results?
(c.) Is it possible to have complete
informaon about the whole, but no
informaon about any of the parts?
Convenonal thought would have us believe
that the answers to these quesons are (a) yes,
(b) no and (c) no. In Quantum Informaon
Science (QIS), though, the answers are just
the opposite: (a) no, (b) yes and (c) yes. While
each of these properes stands in contrast to
our everyday experience, perhaps the most
counterintuive aspect of quantum informaon
is that collecvely they have the potenal to
radically improve the way we transfer, process
and acquire informaon, including but not
limited to the way we communicate, compute
and perform sensing.
Currently though, the most developed
technology oered by QIS is quantum key
distribuon, which provides a way to generate
Keye Martin, Ph.D.
Research Mathematician
Naval Research Laboratory
In Quantum Informaon Science, as in the work above,
the whole can be more than the sum of its parts. (Used
with permission of the arst, specially commissioned for
this arcle)
-
7/28/2019 One + One is Not Two
3/4
Vol. 10 | Spring 2013 www.onr.navy.mil/innovate
9
be copied, and while this poses a denite
challenge when trying to perform certain tasks,
it can also help prevent an eavesdropper from
listening in on quantum communicaon. To
read a qubit, one performs a measurement
on it which yields a classical bit. The result of a
measurement is in general nondeterminisc, somore oen than not we can read two idencal
qubits and obtain dierent results. This might
seem to be completely problemachowever,
if we use a qubit to store informaon and an
aacker manages to steal it, the chances are
good that they will not be able to read the
informaon we want kept secure.
One of the most fascinang properes of
quantum informaon is entanglement. When
two qubits are entangled, measuring one
changes the other, no maer how far apartthe qubits are from each other. In the case of
maximal entanglement (Figure 1), it is possible
to teleport a qubit from one place to another:
the qubit is transferred from point A to point
B without ever travelling through space. With
maximal entanglement, we have complete
informaon about the whole without having
any informaon about the parts i.e. the whole
(2) is more than the sum of its parts (1+1).
A major problem in QIS is dealing with the
environment that a qubit evolves in. This
might be ber, freespace or even water. The
environment is not merely a canvas on to which
a qubit is paintedthe two interact with each
other, oen resulng in noise. Or they may be
entangled, which can cause informaon to be
unwillingly leaked into the environment. Though
usually in smaller doses, even the curvature of
spaceme itself (gravity) can cause noise, which
requires taking relavisc eects into accountimagine a qubit on a satellite orbing Earth for
instance. A major thrust of our groups research
at NRL is to invesgate mathemacal models for
all of these situaons and use them to develop
methods for opmizing performance in a noisy
environment. This research in turn suggests
the possibility of a number of new Naval
technologies. Let us now consider one such
example: using entanglement to enable stealthy
vehicle navigaon under the arcc shelf.
This is a dicult problem because (1) compassesand gyrocompasses are less reliable in higher
latudes, (2) GPS signals cannot penetrate
water and ice, and (3) the shape and thickness
of the ice shelf is variable. To avoid a potenally
catastrophic collision, an underwater arcc
vehicle might use an acve sonar array to
detect its proximity to the ice. In a combat
environment, however, the use of navigaon
sonar could give away the posion of the
vehicle. Our research on QIS has shown that
the operaonal requirements of stealthy
underwater arcc navigaon are tailor-made forentangled qubits. Heres how it works.
Figure 1. With a maximally
entangled state, we have
complete informaon
about the combined
system without having
any informaon about the
individual subsystems.
9
-
7/28/2019 One + One is Not Two
4/4
www.onr.navy.mil/innovate Vol. 10 | Spring 2013
10
Figure 2. By using entangled qubits in place of sonar, it is possible to perform stealthy underwater arcc
navigaon.
target 437 meters away in clear oceanic waters
(Jerlov Type I). For the same signal-to-noise
rao, the detecon probability of a quantum
sensor is 6 mes beer than a laser and 8
mes beer than sonar. Two of the majorchallenges in making this system a reality are
building beer photodetectors and faster
sources of entanglement than presently exist.
In a similar way, we have used entanglement
to design various approaches to radar, lidar,
magnetometry and gravimetry.
The revoluonary potenal of QIS stems
from sciencally re-examining the nature of
informaon itself. But we should not stop with
QIS. There may be other, as of yet undiscovered,
paradigms of informaon. By abstracng the
essenal properes of classical and quantum
informaon, it may be possible to use common
mathemacal structure as a guide in discovering
some of these.n
First, we replace the navigaon sonar array
with a collecon of low brightness quantum
sensors. Then an entangled pair of qubits is
produced; one qubit is kept within the sensor
while the other is emied towards a region ofspace. Aerward, entanglement correlaons
are used to disnguish between noise qubits
and those signal qubits that are bounced back
to the detector due to the presence of a target
(e.g., the ice shelf, the boom, or another
vehicle) (Figure 2). Calculaons performed at
NRL suggest that if this system were built, it
would be capable of operang in low brightness
levels using a small number of qubits and in
an extremely noisy environment, making the
existence of the sensor praccally invisible
to those without access to the entanglementcorrelaons: our quantum sensor hides the
signal qubits in environmental noise, and
entanglement is the key to detect them.
Specically, assuming a signal-to-noise rao
of 2 10-6, a quantum sensor can detect a
www.onr.navy.mil/innovate Vol. 10 | Spring 2013