arXiv subjects

Anil Kumar

Publications and source records attributed to Anil Kumar.

142 records · Page 8Linked to original sources

arXiv2004

Quantum information processing by NMR using a 5-qubit system formed by dipolar coupled spins in an oriented molecule

Quantum Information processing by NMR with small number of qubits is well established. Scaling to higher number of qubits is hindered by two major requirements (i) mutual coupling among qubits and (ii) qubit addressability. It has been demonstrated that mutual coupling can be increased by using residual dipolar couplings among spins by orienting the spin system in a liquid crystalline matrix. In such a case, the heteronuclear spins are weakly coupled but the homonuclear spins become strongly coupled. In such circumstances, the strongly coupled spins can no longer be treated as qubits. However, it has been demonstrated elsewhere, that the $2^N$ energy levels of a strongly coupled N spin-1/2 system can be treated as an N-qubit system. For this purpose the various transitions have to be identified to well defined energy levels. This paper consists of two parts. In the first part, the energy level diagram of a heteronuclear 5-spin system is obtained by using a newly developed heteronuclear z-cosy (HET-Z-COSY) experiment. In the second part, implementation of logic gates, preparation of pseudopure states, creation of entanglement and entanglement transfer is demonstrated, validating the use of such systems for quantum information processing.

quant-ph↗

arXiv2004

Quantum Information processing by NMR: Implementation of Inversion-on-equality gate, Parity gate and Fanout gate

While quantum information processing by nuclear magnetic resonance (NMR) with small number of qubits is well established, implementation of lengthy computations have proved to be difficult due to decoherence/relaxation. In such circumstances, shallow circuits (circuits using parallel computation) may prove to be realistic. Parity and fanout gates are essential to create shallow circuits. In this article we implement inversion-on-equality gate, followed by parity gate and fanout gate in 3-qubit systems by NMR, using evolution under indirect exchange coupling Hamiltonian.

quant-ph↗

arXiv2004

Search for optimum labeling schemes in qubit systems for Quantum Information processing by NMR

Optimal labeling schemes lead to efficient experimental protocols for quantum information processing by nuclear magnetic resonance (NMR). A systematic approach of finding optimal labeling schemes for a given computation is described here. The scheme is described for both quadrupolar systems and spin-1/2 systems. Finally, one of the optimal labeling scheme has been used to experimentally implement a quantum full-adder in a 4-qubit system by NMR, using the technique of transition selective pulses.

quant-ph↗

arXiv2003

Quantum information entropies of the eigenstates and the coherent state of the Pöschl-Teller potential

The position and momentum space information entropies, of the ground state of the Pöschl-Teller potential, are exactly evaluated and are found to satisfy the bound, obtained by Beckner, Bialynicki-Birula and Mycielski. These entropies for the first excited state, for different strengths of the potential well, are then numerically obtained. Interesting features of the entropy densities, owing their origin to the excited nature of the wave functions, are graphically demonstrated. We then compute the position space entropies of the coherent state of the Pöschl-Teller potential, which is known to show revival and fractional revival. Time evolution of the coherent state reveals many interesting patterns in the space-time flow of information entropy.

quant-ph↗

arXiv2003

Quantum Information Processing by NMR using strongly coupled spins

The enormous theoretical potential of Quantum Information Processing (QIP) is driving the pursuit for its practical realization by various physical techniques. Currently Nuclear Magnetic Resonance (NMR) has been the forerunner by demonstrating a majority of quantum algorithms. In NMR, spin systems consisting of coupled nuclear spins are utilized as qubits. In order to carry out QIP, a spin system has to meet two major requirements: (i) qubit addressability and (ii) mutual coupling among the qubits. It has been demonstrated that the magnitude of the mutual coupling among qubits can be increased by orienting the spin-systems in a liquid crystal matrix and utilizing the residual dipolar couplings. While utilizing residual dipolar couplings may be useful to increase the number of qubits, nuclei of same species (homonuclei) might become strongly coupled. In strongly coupled spin-systems, spins loose their individual identity of being qubits. We propose that even such strongly coupled spin-systems can be used for QIP and the qubit-manipulation can be achieved by transition-selective pulses. We demonstrate experimental preparation of pseudopure states, creation of maximally entangled states, implementation logic gates and implementation of Deutsch-Jozsa (DJ) algorithm in strongly coupled 2,3 and 4 spin systems. The energy levels of the strongly coupled 3 and 4 spin systems were obtained by using a Z-COSY experiment.

quant-ph↗

arXiv2003

Implementation of Conditional Phase Shift gate for Quantum Information Processing by NMR, using Transition-selective pulses

Experimental realization of quantum information processing in the field of nuclear magnetic resonance (NMR) has been well established. Implementation of conditional phase shift gate has been a significant step, which has lead to realization of important algorithms such as Grover's search algorithm and quantum Fourier transform. This gate has so far been implemented in NMR by using coupling evolution method. We demonstrate here the implementation of the conditional phase shift gate using transition selective pulses. As an application of the gate, we demonstrate Grover's search algorithm and quantum Fourier transform by simulations and experiments using transition selective pulses.

quant-ph↗

arXiv2003

A fast method for the measurement of long spin-lattice relaxation times by Single Scan Inversion Recovery experiment

A new method of measuring long spin-lattice relaxation times ($T_1$) is proposed. Being a single scan technique, the method is at least one order of magnitude faster than the conventional technique. This method (Single-Scan or Slice Selected Inversion Recovery or SSIR) relies on the slice selection technique. The method is experimentally verified and compared with the time taken by the conventional measurement. Furthermore, it is shown that the conventional Inversion Recovery (IR) method which suffers from effects of r.f. inhomogeneity can also be improved by measuring the magnetization of only a central slice.

cond-mat.soft↗

arXiv2003

Contents of Physics Related E-Print Archives

The frontiers of physics related e-print archives (1994-2002) at http://www.arxiv.org/archives/physics web service are explored from 7770 submissions. No. of e-prints in the six research disciplines besides physics (5390) were: Condensed matter(754), Quantum physics(279), Astrophysics(222), Chemical physics(129), High energy physics Phenomenology(118), and High energy physics-Theory(100)). By keyword contents following major sub-fields have high frequency: Atomic physics(1258), General physics(1121), Chemical physics(892), Accelerator physics(769), Optics(686), Biological physics(674), and Computational physics(607). Interdomainary co-word cluster analysis revealed higher e-print contents for: Classical physics-General physics(108), Quantum physics-Optics(53), and High energy physics (Phenomenology)Atomic physics(49). Prominent contributors were B. G. Sidharth (India), V. V. Flambaum (Australia), Antonina N. Fedorova (Russia), and Michael G. Zeitlin (Russia).

physics.data-an↗

arXiv2003

Quantum Information processing by NMR: Preparation of pseudopure states and implementation of unitary operations in a single-qutrit system

Theoretical Quantum Information Processing (QIP) has matured from the use of qubits to the use of qudits (systems having states> 2). Where as most of the experimental implementations have been performed using qubits, little experimental work has been carried out using qudits as yet. In this paper we demonstrate experimental realization of a qutrit system by nuclear magnetic resonance (NMR), utilizing deuterium (spin-1) nuclei partially oriented in liquid crystalline phase. Preparation of pseudopure states and implementation of unitary operations are demonstrated in this single-qutrit system, using transition selective pulses.

quant-ph↗

arXiv2003

Serving Database Information Using a Flexible Server in a Three Tier Architecture

The D0 experiment at Fermilab relies on a central Oracle database for storing all detector calibration information. Access to this data is needed by hundreds of physics applications distributed worldwide. In order to meet the demands of these applications from scarce resources, we have created a distributed system that isolates the user applications from the database facilities. This system, known as the Database Application Network (DAN) operates as the middle tier in a three tier architecture. A DAN server employs a hierarchical caching scheme and database connection management facility that limits access to the database resource. The modular design allows for caching strategies and database access components to be determined by runtime configuration. To solve scalability problems, a proxy database component allows for DAN servers to be arranged in a hierarchy. Also included is an event based monitoring system that is currently being used to collect statistics for performance analysis and problem diagnosis. DAN servers are currently implemented as a Python multithreaded program using CORBA for network communications and interface specification. The requirement details, design, and implementation of DAN are discussed along with operational experience and future plans.

cs.DC↗

arXiv2003

Use of Quadrupolar Nuclei for Quantum Information processing by Nuclear Magnetic Resonance: Implementation of a Quantum Algorithm

Physical implementation of Quantum Information Processing (QIP) by liquid-state Nuclear Magnetic Resonance (NMR), using weakly coupled spin-1/2 nuclei of a molecule, is well established. Nuclei with spin$>$1/2 oriented in liquid crystalline matrices is another possibility. Such systems have multiple qubits per nuclei and large quadrupolar couplings resulting in well separated lines in the spectrum. So far, creation of pseudopure states and logic gates have been demonstrated in such systems using transition selective radio-frequency pulses. In this paper we report two novel developments. First, we implement a quantum algorithm which needs coherent superposition of states. Second, we use evolution under quadrupolar coupling to implement multi qubit gates. We implement Deutsch-Jozsa algorithm on a spin-3/2 (2 qubit) system. The controlled-not operation needed to implement this algorithm has been implemented here by evolution under the quadrupolar Hamiltonian. This method has been implemented for the first time in quadrupolar systems. Since the quadrupolar coupling is several orders of magnitude greater than the coupling in weakly coupled spin-1/2 nuclei, the gate time decreases, increasing the clock speed of the quantum computer.

quant-ph↗

arXiv2002

Efficient Quantum State Tomography for Quantum Information Processing using a two-dimensional Fourier Transform Technique

A new method of quantum state tomography for quantum information processing is described. The method based on two-dimensional Fourier transform technique involves detection of all the off-diagonal elements of the density matrix in a two-dimensional experiment. All the diagonal elements are detected in another one-dimensional experiment. The method is efficient and applicable to a wide range of spin systems. The proposed method is explained using a 2 qubit system and demonstrated by tomographing arbitrary complex density matrices of 2 and 4 qubit systems using simulations.

quant-ph↗

arXiv2000

Quantum Computing by Two-Dimensional NMR using Spin- and Transition-Selective Pulses

Quantum computing using two-dimensional NMR has recently been described using scalar coupling evolution technique [J. Chem. Phys.,109,10603 (1998)]. In the present paper, we describe two-dimensional NMR quantum computing with the help of selective pulses. A number of logic gates are implemented using two and three qubits with one extra observer spin. Some many-in-one gates (or Portmanteau gates) are implemented. Toffoli gate (or AND/NAND gate) and OR/NOR gates are implemented on three qubits. Deutsch-Jozsa quantum algorithm for one and two qubits, using one extra work qubit, has also been implemented using selective pulses after creating a coherent superposition state, in the two-dimensional methodology.

quant-ph↗

arXiv2000

Implementation of a Deutsch-like quantum algorithm utilizing entanglement at the two-qubit level, on an NMR quantum information processor

We describe the experimental implementation of a recently proposed quantum algorithm involving quantum entanglement at the level of two qubits using NMR. The algorithm solves a generalisation of the Deutsch problem and distinguishes between even and odd functions using fewer function calls than is possible classically. The manipulation of entangled states of the two qubits is essential here, unlike the Deutsch-Jozsa algorithm and the Grover's search algorithm for two bits.

quant-ph↗

arXiv2000

Implementing quantum logic operations, pseudo-pure states and the Deutsch-Jozsa algorithm using non-commuting selective pulses in NMR

We demonstrate experimentally the usefulness of selective pulses in NMR to perform quantum computation. Three different techniques based on selective pulse excitations have been proposed to prepare a spin system in a pseudo-pure state. We describe the design of novel ``portmanteau'' gates using the selective manipulation of level populations. A selective pulse implementation of the Deutsch-Jozsa algorithm for a two-qubit and a three-qubit quantum computer is demonstrated.

quant-ph↗

arXiv1999

Quantum entanglement in the NMR implementation of the Deutsch-Jozsa algorithm

A scheme to execute an n-bit Deutsch-Jozsa (D-J) algorithm using n qubits has been implemented for up to three qubits on an NMR quantum computer. For the one and two bit Deutsch problem, the qubits do not get entangled, hence the NMR implementation is achieved without using spin-spin interactions. It is for the three bit case, that the manipulation of entangled states becomes essential. The interactions through scalar J-couplings in NMR spin systems have been exploited to implement entangling transformations required for the three bit D-J algorithm.

quant-ph↗