
BMe Research Grant 

BMe Research Grant  2010
3^{rd} Prize
Quantum
computing offers revolutionary solutions in the field of computer sciences,
applying tools of quantum physics, which are incomparably numerous than those of
classical physics. Although quantum computers merely promise applications
for the far future, a few algorithms are already available for solving problems otherwise difficult to handle with traditional computers. Today's
telecommunication requires large amount of data transfer via satellites. An
interesting way of dealing with this problem might be using quantum
communication. Unlike the optical cablebased, wired quantum solutions, quantum satellite communication requires a freespace channel, which is
affected by various physical factors. Over the last years, we have developed a mathematical
model for examining satellite quantum communications. We have analysed the
redundancyfree quantum channel and developed redundancyfree quantum
codes.
Mobile
Communication and Computing Laboratory at BME Department of Telecommunications has been
working on wireless and mobile systems for more than 10 years. Under the
leadership of Dr. Imre Sándor, several members of the laboratory have started dealing
with quantum informatics and numerous publications have been completed since
2003. At present, and three PhD dissertations are
in process.
In 1965, Gordon Moore studied the number of transistors that can be placed inexpensively on an integrated circuit[1]. The big question is that how long this trend – i.e the increase in the number of transistors – is going to continue?
Researches offer different solutions to this problem, e.g. use of parallel
computers, DNStechnology or informatics based on quantum mechanics. Why quantum
mechanics? To allocate more transistors on an integrated circuit of a
given size, the size of individual transistors have to be reduced. At one point, we will
cross the borderline of atomic dimensions, where classical EbersMoll
equals are not valid anymore, and quantum mechanical models have to be used
instead [2].
Why are quantumbased approaches better than the classical ones? The power
of quantum
parallelism allows us to solve classically complex problems during a short
period of time. Groveralgorithm provides more efficient searches in unsorted databases [1].
We can build different quantum circuits and decrypt the keys of RSA with
the help of Shoralgorithm[2]. Quantum
cryptography provides new ways of transmitting information securely (BB84 and B92
protocols) [3]. In quantum
teleportation we use entangled pairs to
transport information between two points [4].
Freespace Quantum Key Distribution (QKD) was first implemented over an optical path of about 30 cm in 1991 [5]. In 2002, a research group demonstrated that freespace QKD is possible in daylight [6]. In 2006, the distance was further extended to 144 km by an international research group [7]. In 2008, the European Space Agency named the quantumbased satellite communication as one of the most important targets for the next five years. A European consortium aims at establishing a spacetoEarth quantumbased communication experiment from the International Space Station [8].
Freespace quantum communication can be extended to
groundtosatellite or satellitesatellite quantum communication [9]. One of the
main advantages of using space for future quantum communication is achieving the level of lossfree and distortionfree optical communication. We have examined two
different protocols – the superdense coding [1]
and the BB84
[3].
Another interesting question is related to quantum error correction. Currently many techniques are introduced but in these proposals redundancy is required for successful error correction. If we could use redundancyfree solutions, they would be very useful in the longdistance aerial communication, eliminating the need for redundant error correction codes used nowadays.
At present, using optical QKD is limited to a distance of appr. 100 km, however, freespace quantum cryptography makes it possible transmitting photons over long distances. We examined the physical properties of the Earthspace and spacespace channels to give some prescriptions about the possible losses and to give some useful ideas about the implementation of such a channel [10, 11]. We also developed an analytical model which describes one photon’s (or a few photons’) behavior to simulate the communication process over a satellite quantum channel. Our model enables us to analyze and determine the parameter requirements to the implementation of a satellite quantum channel for Earthsatellite and satellitesatellite communication.
In a best case scenario of superdense coding,
Alice and Bob already share an entangled qubit pair, and thus every qubit sent by
Alice and arriving at Bob’s detector carries two bits of information. In the
statistical sense, the protocol is not worthwhile if more than half of the qubits
sent by Alice is not detected (in other words, if the transmittance is lower than
0.5). In this case, strong signals and classical protocols perform
better.
The most famous flexible asymmetrical protocol is the BB84
protocol. It is important to examine the performance and limits of
cryptography based on BB84 in various environments as well as to know the noise
parameters of the quantum channel, as errors appearing in the received quantum bits allow us to discover an eavesdropper.
We also used the analytical
methods to study the freespace quantum channel. Analytical
solutions were applied for constructing error coding methods to support redundancyfree
approaches.
Based on our mathematical models, we were able to examine selected parameters
of quantum satellite communication. According to our results, the distance
between two satellites should be maximum 15,000 km to handle a successful BB84. These
results show that we can realize quantum communication over intercontinental
distances. However, after analyzing of LEO (Low Earth
Orbit) and GEO
(Geostationary Earth Orbit) satellite orbit, we can say that a BB84
supported equipment running on a LEO satellite cannot reach a GEO
satellite.
Another important question is how fast the satellites can
exchange keys with the BB84 depending on the distances. (The BB84 key
distribution protocol was published by Charles
H. Bennett and Gilles Bassard in 1984.
The algorithm working in wired system is a commercial product. Efficiency of
the freespace quantum channel is examined by this protocol.) We have shown that
the LEO orbits are better for the BB84. However, we extended our examinations to
the superdense coding algorithms, as well. (In superdense coding algorithm, we
need to send only one quantum bit instead of two classical bits.) According to
our results, superdense coding in a best case scenario is only worthwhile in
clear weather, at low zenith angles and for large detector mirror
sizes.
In another research, we would like to provide error correction by sending certain amount of qubits over a noisy quantum channel. The qubits are independent and each contains information that needs to be processed. We developed different redundancyfree solutions for freespace quantum communication.
We started with a special unitary channel, where the information itself was
classical, coded into qubits. The channel transforms a unitary transformation
with p probability and an identity transformation with 1p probability. We can
construct an error coding description in which the classical states are coded
into the eigenvectors of the matrix of the unitary channel. We have shown that this
errorcoding construction leads to a redundancyfree solution because we can
restore one quantum bit sent over the channel without any other (redundant)
information.
In the next step, we considered the redundancyfree implementation of a unitary error correcting operator. The protocol achieves the redundancyfree quantum communication using local unitary operations and unitary matrices. Our research is important because using these redundancyfree techniques effective capacity of the satellite link could be increased..
Examining the connection of quantum informatics and satellite communication back in 2003 meant starting to deal with a field which gained more and more importance.
Our research area is even more interesting because it combines results of
mathematical modeling, information theory and engineering.
We have received
more article review requests. In this year we were invited to submit two
different book chapters.
In our further research, we would like to study the way can use entangled
pairs in redundancyfree coding. In another research topic, we examine how we
can improve selfadapting communication networks through the application of quantuminformaticsbased solutions.
Publications
International journal articles
Laszlo Bacsardi
Satellite Communication Over Quantum
Channel
ACTA ASTRONAUTICA 61:(1–6) pp. 151–159.
(2007)
Laszlo Bacsardi
Using Quantum Computing Algorithms
in Future Satellite Communication
ACTA ASTRONAUTICA 57:(2–8) pp. 224–229.
(2005)
International book chapters
Laszlo Bacsardi, Sandor Imre
QuantumBased Information Transfer in
Satellite Communication
Book: „Satellite Communications”, ISBN
9789537619XX, Sciyo (accepted, to appear)
Laszlo
Bacsardi, Laszlo Gyongyosi, Marton Berces, Sandor Imre
Quantum Solutions
for Future Space Communication
Book: „Quantum Computers”, Nova Science
Publishers (accepted, to appear)
Laszlo Bacsardi, Laszlo
Gyongyosi, Sandor Imre
Solutions for RedundancyFree Error Correction in
Quantum Channel
LECTURE NOTES OF THE INSTITUTE FOR COMPUTER SCIENCES
SOCIALINFORMATICS AND TELECOMMUNICATIONS ENGINEERING 36: pp. 117–124.
(2010)
International conference papers
Mate Galambos, Laszlo Bacsardi, Sandor Imre
Modeling and Analyzing
the QuantumBased EarthSatellite and SatelliteSatellite
Communications
International Astronautical Congress 2010
(accepted)
L. Bacsardi, L. Gyongyosi, S. Imre
Using
Redundancyfree Quantum Channels for Improving the Satellite
Communication
In: Proceedings CD of 2nd International ICST Conference on
Personal Satellite Services. Rome, Italy, 2010.02.04–2010.02.05., pp.
1–14. Paper 8560.
L Bacsardi, L Gyongyosi, S Imre
Solutions
for RedundancyFree Error Correction in Quantum Channel
In: Proceedings
CD of 1st International ICST Conference on Quantum Communication and Quantum
Networking. Vico Equense, Italy, 2009.10.26–2009.10.30., Gent: pp. 1–8.
Paper 8077. (ISBN: 9789639799837)
L. Bacsárdi, M. Bérces,
S. Imre
RedundancyFree Quantum TheoryBased Error Correction Method in Long
Distance Aerial Communication.
In: 59th International Astronautical
Congress, IAC Proceedings 2008. Glasgow,Great Britain, 2008.09.29–2008.10.03.
pp. 1–7. Paper IAC08B2.4.8.
Hungarian journal articles
László Bacsárdi, Máté Galambos, Sándor Imre
Quantum channel in
Earthsatellite and satellitesatellite communications
HÍRADÁSTECHNIKA
LXV:(3–4.) pp. 23–29. (2010)
Scientific lectures (in Hungarian)
László Bacsárdi
Teleporting with the speed of light – adventures in
the world of quantum informatics
Future's techniques, techniques from the
future, Sopron, Apr 14, 2010
László Bacsárdi, Sándor
Imre
The mistery of the root NOT gate  will have Mr. Moore a good night on
tomorrow?
Puskás Tivadar Távközlési Technikum, Budapest, March 29,
2010
László Bacsárdi
Using quantum informatics in
space telecommunication  could ET make a homecall faster than the speed of
light?
Gyula Fényi Astronomical Open University, Sopron, Nov 23,
2007
Links
Website of our university
lecture  Quantum Informatics and Communications
Selected web portals
Quantiki
Virtual Journal of Quantum
Information
The International Nanoscience Communicity
Quantum companies
id
Quantique (sells Quantum Key Distribution products)
MagiQ
Technologies (sells quantum devices for cryptography)
Quintessence Labs Solutions (based
on continuous wave lasers)
References
[1] S. Imre, B. Ferenc, ‘Quantum Computing and Communications: An Engineering
Approach’, (Wiley, 2005)
[2] Michael A. Nielsen, IsaacL. Chuang, ’Quantum
Computation and Quantum Information’ (Cambridge University Press, 2000)
[3]
Charles H. Benett, Gilles Bassard, ’Quantum Chryptography: Public Key
Distribution and Coin Tossing’, Internation Conference on Computers, Systems
& Signal Processing, Bangalore, India (December 10–12, 1984)
[4]
Teleporting an Unknown Quantum State via dual Classical and
EinsteinPodolskyRosen Channels, C. H. Bennett, G. Brassard, C. Crépeau, R.
Jozsa, A. Peres, W. K. Wooters, (Phys. Rev. Lett, vol. 70, n 13, pp. 1895, March
1993)
[5] C. H. Bennett et al., Lecture Notes In Computer Science 473, 253
(1991).
[6] Richard J. Hughes, Jane E. Nordholt, Derek Derkacs and Charles G.
Peterson, Practical freespace quantum key distribution over 10 km in daylight
and at night, (New Journal of Physics 4 (2002) 43.1–43.14 )
[7] Tobias
SManderbach, et al., ’Experimetal Demostration of FreeSpace DecoyState
Quantum Key Distribution over 144km’, Phys. Rev. Lett. 98, 010504 (2007)
[8]
Josep Maria Predigues Armengol, et al., ’Quantum Communications at ESA: Towards
a space experiment on the ISS’, Acta Astronautica 63, 165–178 (2008)
[9] L.
Bacsardi, Satellite Communication Over Quantum Channel., Acta Astronautica
61:(1–6) pp. 151–159, 2007
[10] Larry C. Andrews and Ronald L. Phillips, ’
Laser Beam Propagation through Random Media’, (SPIE Press Book, 2005)
[11] C.
Bonato et al., ’Polarization transformation induced on qubits in a
SpacetoEarth quantum communication link’, Quantum Electronics and Laser
Science Conference (2007)
Source of the figures: Wikipedia, freetouse pictures, official logo of
the Mobile Communication and Computing Laboratory, selfmade
figures.