56 | New Scientist | 14 March 2020
The back pages Q&A
FUNKYFOOD LONDON-PAUL WILLIAMS/ALAMYSo, what do you do?
I work with photons, investigating their use
as building blocks for quantum technologies.
These could revolutionise our lives due to
their promise for exponential speed-ups in
computing and unprecedented security in
communications. One of our current projects
involves quantum communication between
two continents using a satellite.The triple-slit experiment sounds
interesting, what is it?
The double-slit experiment shows that photons
act both as waves and as particles, but it also
suggests that a single photon passes through
both slits at the same time, a phenomenon called
superposition. We devised a way to test if that was
really happening with the triple-slit experiment.
What we found suggests that we need to update
our view of superposition and further experiments
could potentially even question quantum
mechanics. It also paves the way for higher
dimensional quantum information science.What do you mean by higher dimensional
quantum information science?
Up to now, the focus has been on quantum bits,
or qubits, which have two base states. We are
working on higher dimensional systems such
as qutrits, which have three base states. Triple
slits provide a natural system wherein we have
three modes of a single photon, forming a
three-dimensional qutrit.What would be different about a quantum
computer using qutrits?
While everyone is excited about having 50 qubits
together, the same outcome can be achieved with
a smaller number of qutrits. This may help us
develop quantum computers with greater power.How has your field of study changed in
the time you have been working in it?
Wow, a lot. When I first set up my lab in India
in 2012, there was scepticism galore, both about
quantum technologies and fundamental studies
in quantum mechanics. Now, fundamental tests
are the bedrock for modern quantum technologies
and quantum computing is the in thing.Did you have to overcome any particular
challenges to get where you are today?
I sometimes wish I belonged to a different gender
and had more grey hair. That can help in being
considered seriously as well as with recognition.
Having said that, why should I change? Let the
world change its viewpoint!If you could have a long conversation with any
scientist, living or dead, who would it be?
One would be Marie Curie. I would ask her how
she managed to be who she was and do what
she did in spite of being a woman and living in a
different era. I would also like to talk to Max Born.
Our experiment was the first ever test of the Born
rule, which predicts the probability of a photon’s
location after passing through three slits. I would
like to know his opinion on our experiment.You did the triple-slit experiment in a
cornfield. Why?
Well, students get hungry! On a more serious
note, the cornfield provided a natural anechoic
chamber – in other words, one devoid of
reflections from metal etc. – which is necessary
for the precision experiment we performed. We
also required a considerable amount of space for
the experiment. We found out that corn is a great
absorber of microwaves, too.What scientific development do you hope
to see in your lifetime?
A quantum computer that is powerful enough to
break existing encryption systems, so our research
on secure quantum communications becomes
useful in my lifetime.How useful will your skills be after the
apocalypse?
Aha, you are assuming that my skills will outlive
the apocalypse! Surely, that proves the point
regarding their perceived usefulness? However,
if practical quantum computing indeed becomes
a reality by then, maybe we will find a way to
survive the apocalypse simply through some
mind-boggling simulations, which are currently
difficult to fathom. Who knows? ❚Urbasi Sinha is a professor of quantum physics at
the Raman Research Institute in Bangalore, India“The results
of the triple-slit
experiment
could question
quantum
mechanics
itself”
The double-slit experiment has long
been the cornerstone of quantum
physics. Now Urbasi Sinha’s triple-slit
variant could usher in an era of higher-
dimensional quantum computing