David Tong talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of
Article: Local blockade of Rydberg excitation in an
D;Farooqi, SM;Stanojevic, J;Krishnan, S;Zhang,
YP;Cote, R;Eyler, EE;Gould, PL
Journal: PHYS REV LETT, 93 (6): art. no.-063001, AUG 6
Addresses: Univ Connecticut, Dept Phys, Storrs, CT 06269
Univ Connecticut, Dept Phys, Storrs, CT 06269 USA.
Why do you think your paper is highly
The possibility of a computer that operates on the principle of quantum
mechanics has attracted growing interest across many research fields. Just
within the past decade, we have seen many advances in the field of quantum
information. Numerous implementations to build quantum phase gates have
been proposed, one of which is using trapped neutral atoms which offer many
advantages: there are already well-developed techniques for the cooling and
trapping of neutral atoms, such as far-off-resonance traps (FORT),
microtraps, optical lattices, and so on. The ground states of neutral atoms
hardly interact with the environment, giving rise to very long coherence
times, and the strong interactions of highly excited Rydberg states allows
information to be exchanged quickly before decoherence sets in.
On the other hand, creating quantum phase gates from microscopic samples of
these neutral atoms and addressing these microscopic qubits individually
pose extreme experimental challenges. An exceptional degree of control over
submicron systems would be necessary to address a single qubit. Our paper
demonstrates a new experimental technique to work around these challenges.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
"Our work exhibits a new method to
create and address quantum phase gates using
trapped neutral atoms."
Through this work, we offer the experimental realization of a theoretical
work developed in 2001 (MD Lukin, et al., Phys. Rev.
Lett. 87, 037901). Our work exhibits a new method to create and
address quantum phase gates using trapped neutral atoms.
By exploiting the strong interactions of the high Rydberg states, we are
able to show a coherent manipulation of quantum information stored in these
collective excitations of mesoscopic many-atom ensembles. The strong
interactions shift the Rydberg levels of other nearby atoms and prevent (or
blockade) them from being excited. This blockading mechanism causes the
mesoscopic ensemble to behave as a single super-atom and thus, many
stringent requirements for the implementation of quantum gates can be
Would you summarize the significance of your paper
in layman's terms?
Quantum computers would rely on the operation of quantum gates, which pose
experimental challenges since extremely high control over the size of an
atom would be required. Our work alleviates many of these experimental
difficulties. The blockading mechanism allows us to address many atoms at
once, with the end result being as if we were to address one of them
individually. We can now work with many atoms, rather than having to
address a single atom, yet we can still expect the behavior of a single
How did you become involved in this research and
were there any particular problems encountered along the way?
This work was done under the supervision of three Principal Investigators
in the Department of Physics at the University of Connecticut: Dr. Phillip
Gould and Dr. Edward Eyler on the experimental side, and Dr. Robin
Côté giving support on the theoretical side. I primarily work
on the experimental side as part of my Ph.D. research. This work relies on
the observation of suppression in signal size and thus, we spend an
elaborate amount of time and effort to ensure that we are free from any
We also spend considerable amounts of time choosing and calibrating our
detection mechanism to enable us to detect small signals with confidence,
apart from all the background/noise we have in the system. Once we are
confident that we have the detection mechanism we need and that our signals
are free from any possible saturation effect, we are able to complete the
entire experiment within a relatively short period of time.
Where do you see your research leading in the
The blockading mechanism is part of the work leading towards having quantum
phase gates based on mesoscopic samples of neutral atoms. There are still
other things that need to be done, e.g., making sure that we have uniform
density in our sample, making sure that we are able to detect a signal from
a single atom, etc.
Do you foresee any social or political implications
for your research?
Probably not with this particular work, but there will be some implications
within the field of quantum information as a whole. Even though quantum
computation is still in its early phases, we should already make
preparations and adjustments towards the realization of quantum
computation. For example, the RSA encryption and decryption, which is based
on the factorization of large numbers, have been proven to be good enough
as the best algorithm available on the current classical computers, yet can
only solve the factorization problem in exponential time.
However, the quantum algorithm (e.g., as developed by Peter Shor, the Morss
Professor of Applied Mathematics at MIT) can efficiently factor large
numbers (with more than 100 digits or so) in polynomial time, a very
significant improvement. The current strongest encryption and decryption
may prove to be insufficient if quantum computation were available today.
David Tong, Ph.D. Candidate
University of Connecticut
Storrs, CT, USA
Keywords: quantum mechanics, quantum information,
quantum computation, quantum phase gates, far-off-resonance traps,
microtraps, optical lattices, highly excited rydberg states, high rydberg
states, the quantum algorithm, peter shor.