4,643 research outputs found
Quantum error correction in crossbar architectures
A central challenge for the scaling of quantum computing systems is the need
to control all qubits in the system without a large overhead. A solution for
this problem in classical computing comes in the form of so called crossbar
architectures. Recently we made a proposal for a large scale quantum
processor~[Li et al. arXiv:1711.03807 (2017)] to be implemented in silicon
quantum dots. This system features a crossbar control architecture which limits
parallel single qubit control, but allows the scheme to overcome control
scaling issues that form a major hurdle to large scale quantum computing
systems. In this work, we develop a language that makes it possible to easily
map quantum circuits to crossbar systems, taking into account their
architecture and control limitations. Using this language we show how to map
well known quantum error correction codes such as the planar surface and color
codes in this limited control setting with only a small overhead in time. We
analyze the logical error behavior of this surface code mapping for estimated
experimental parameters of the crossbar system and conclude that logical error
suppression to a level useful for real quantum computation is feasible.Comment: 29 + 9 pages, 13 figures, 9 tables, 8 algorithms and 3 big boxes.
Comments are welcom
A Tight Bound for Probability of Error for Quantum Counting Based Multiuser Detection
Future wired and wireless communication systems will employ pure or combined
Code Division Multiple Access (CDMA) technique, such as in the European 3G
mobile UMTS or Power Line Telecommunication system, but also several 4G
proposal includes e.g. multi carrier (MC) CDMA. Former examinations carried out
the drawbacks of single user detectors (SUD), which are widely employed in
narrowband IS-95 CDMA systems, and forced to develop suitable multiuser
detection schemes to increase the efficiency against interference. However, at
this moment there are only suboptimal solutions available because of the rather
high complexity of optimal detectors. One of the possible receiver technologies
can be the quantum assisted computing devices which allows high level
parallelism in computation. The first commercial devices are estimated for the
next years, which meets the advert of 3G and 4G systems. In this paper we
analyze the error probability and give tight bounds in a static and dynamically
changing environment for a novel quantum computation based Quantum Multiuser
detection (QMUD) algorithm, employing quantum counting algorithm, which
provides optimal solution.Comment: presented at IEEE ISIT 2002, 7 pages, 2 figure
Implications of Electronics Constraints for Solid-State Quantum Error Correction and Quantum Circuit Failure Probability
In this paper we present the impact of classical electronics constraints on a
solid-state quantum dot logical qubit architecture. Constraints due to routing
density, bandwidth allocation, signal timing, and thermally aware placement of
classical supporting electronics significantly affect the quantum error
correction circuit's error rate. We analyze one level of a quantum error
correction circuit using nine data qubits in a Bacon-Shor code configured as a
quantum memory. A hypothetical silicon double quantum dot quantum bit (qubit)
is used as the fundamental element. A pessimistic estimate of the error
probability of the quantum circuit is calculated using the total number of
gates and idle time using a provably optimal schedule for the circuit
operations obtained with an integer program methodology. The micro-architecture
analysis provides insight about the different ways the electronics impact the
circuit performance (e.g., extra idle time in the schedule), which can
significantly limit the ultimate performance of any quantum circuit and
therefore is a critical foundation for any future larger scale architecture
analysis.Comment: 10 pages, 7 figures, 3 table
Simulating chemistry efficiently on fault-tolerant quantum computers
Quantum computers can in principle simulate quantum physics exponentially
faster than their classical counterparts, but some technical hurdles remain.
Here we consider methods to make proposed chemical simulation algorithms
computationally fast on fault-tolerant quantum computers in the circuit model.
Fault tolerance constrains the choice of available gates, so that arbitrary
gates required for a simulation algorithm must be constructed from sequences of
fundamental operations. We examine techniques for constructing arbitrary gates
which perform substantially faster than circuits based on the conventional
Solovay-Kitaev algorithm [C.M. Dawson and M.A. Nielsen, \emph{Quantum Inf.
Comput.}, \textbf{6}:81, 2006]. For a given approximation error ,
arbitrary single-qubit gates can be produced fault-tolerantly and using a
limited set of gates in time which is or ; with sufficient parallel preparation of ancillas, constant average
depth is possible using a method we call programmable ancilla rotations.
Moreover, we construct and analyze efficient implementations of first- and
second-quantized simulation algorithms using the fault-tolerant arbitrary gates
and other techniques, such as implementing various subroutines in constant
time. A specific example we analyze is the ground-state energy calculation for
Lithium hydride.Comment: 33 pages, 18 figure
4. generációs mobil rendszerek kutatása = Research on 4-th Generation Mobile Systems
A 3G mobil rendszerek szabványosítása a végéhez közeledik, legalábbis a meghatározó képességek tekintetében. Ezért létfontosságú azon technikák, eljárások vizsgálata, melyek a következő, 4G rendszerekben meghatározó szerepet töltenek majd be. Több ilyen kutatási irányvonal is létezik, ezek közül projektünkben a fontosabbakra koncentráltunk. A következőben felsoroljuk a kutatott területeket, és röviden összegezzük az elért eredményeket. Szórt spektrumú rendszerek Kifejlesztettünk egy új, rádiós interfészen alkalmazható hívásengedélyezési eljárást. Szimulációs vizsgálatokkal támasztottuk alá a megoldás hatékonyságát. A projektben kutatóként résztvevő Jeney Gábor sikeresen megvédte Ph.D. disszertációját neurális hálózatokra épülő többfelhasználós detekciós technikák témában. Az elért eredmények Imre Sándor MTA doktori disszertációjába is beépültek. IP alkalmazása mobil rendszerekben Továbbfejlesztettük, teszteltük és általánosítottuk a projekt keretében megalkotott új, gyűrű alapú topológiára épülő, a jelenleginél nagyobb megbízhatóságú IP alapú hozzáférési koncepciót. A témakörben Szalay Máté Ph.D. disszertációja már a nyilvános védésig jutott. Kvantum-informatikai módszerek alkalmazása 3G/4G detekcióra Új, kvantum-informatikai elvekre épülő többfelhasználós detekciós eljárást dolgoztunk ki. Ehhez új kvantum alapú algoritmusokat is kifejlesztettünk. Az eredményeket nemzetközi folyóiratok mellett egy saját könyvben is publikáltuk. | The project consists of three main research directions. Spread spectrum systems: we developed a new call admission control method for 3G air interfaces. Project member Gabor Jeney obtained the Ph.D. degree and project leader Sandor Imre submitted his DSc theses from this area. Application of IP in mobile systems: A ring-based reliable IP mobility mobile access concept and corresponding protocols have been developed. Project member Máté Szalay submitted his Ph.D. theses from this field. Quantum computing based solutions in 3G/4G detection: Quantum computing based multiuser detection algorithm was developed. Based on the results on this field a book was published at Wiley entitled: 'Quantum Computing and Communications - an engineering approach'
- …