Coding for the Optical Channel: the Ghost-Pulse Constraint

We consider a number of constrained coding techniques that can be used to mitigate a nonlinear effect in the optical fiber channel that causes the formation of spurious pulses, called ``ghost pulses.'' Specifically, if $b_1 b_2 ... b_{n}$ is a sequence of bits sent across an optical channel, such that $b_k=b_l=b_m=1$ for some $k,l,m$ (not necessarily all distinct) but $b_{k+l-m} = 0$, then the ghost-pulse effect causes $b_{k+l-m}$ to change to 1, thereby creating an error. We design and analyze several coding schemes using binary and ternary sequences constrained so as to avoid patterns that give rise to ghost pulses. We also discuss the design of encoders and decoders for these coding schemes.Comment: 13 pages, 6 figures; accepted for publication in IEEE Transactions on Information Theor

Conditional Quantum Dynamics and Logic Gates

Quantum logic gates provide fundamental examples of conditional quantum dynamics. They could form the building blocks of general quantum information processing systems which have recently been shown to have many interesting non--classical properties. We describe a simple quantum logic gate, the quantum controlled--NOT, and analyse some of its applications. We discuss two possible physical realisations of the gate; one based on Ramsey atomic interferometry and the other on the selective driving of optical resonances of two subsystems undergoing a dipole--dipole interaction.Comment: 5 pages, RevTeX, two figures in a uuencoded, compressed fil

Photon temporal modes: a complete framework for quantum information science

Field-orthogonal temporal modes of photonic quantum states provide a new framework for quantum information science (QIS). They intrinsically span a high-dimensional Hilbert space and lend themselves to integration into existing single-mode fiber communication networks. We show that the three main requirements to construct a valid framework for QIS -- the controlled generation of resource states, the targeted and highly efficient manipulation of temporal modes and their efficient detection -- can be fulfilled with current technology. We suggest implementations of diverse QIS applications based on this complete set of building blocks.Comment: 17 pages, 13 figure

Implementation of a three-qubit quantum error correction code in a cavity-QED setup

The correction of errors is of fundamental importance for the development of contemporary computing devices and of robust communication protocols. In this paper we propose a scheme for the implementation of the three-qubit quantum repetition code, exploiting the interaction of Rydberg atoms with the quantized mode of a microwave cavity field. Quantum information is encoded within two circular Rydberg states of the atoms and encoding and decoding process are realized within two separate microwave cavities. We show that errors due to phase noise fluctuations could be efficiently corrected using a state-of-the-art apparatus.Comment: 9 pages, 5 figures. This is v2. Some misprints corrected, conclusions section extended, refs added. Accepted for publication on PR

Demonstrating multilevel entanglement and optimal quantum measurements

Optimal generalised quantum measurements are important for quantum information applications in both photonic and solid state systems. However, until now, the implementations of such measurements have been optical. Entanglement is also a very important resource in quantum communication and information processing. However, highdimensional entangled states and corresponding Bell-inequality violations are challenging to detect and demonstrate experimentally. This thesis focuses on these two aspects of signal detection. A cavity quantum electrodynamics (QED) scheme to realise an optimised quantum measurement demonstrating the superadditivity of quantum channel capacity is proposed and analysed. The measurement is shown to be feasible using atoms in a cavity QED setup even in the presence of rather high levels of experimental errors. This is interesting because cavity QED realisations could potentially be more easily scaled to increase quantum coding gain. Experimental unambiguous discrimination between non-orthogonal states is also carried out for the first time in the solid state using the nuclear spin of a nitrogen atom associated with a defect in bulk diamond—an important step for implementations of solid-state quantum computing. This thesis presents a method for verifying entanglement dimension using only Bell inequality test measurements. It also shows experimental results demonstrating genuine eleven-dimensional two-photon orbital angular momentum (OAM) entanglement and violations of generalised Bell inequalities up to dimension twelve. The demonstrated highdimensional entanglement is potentially useful for closing the detection loophole in Belltest experiments and for real-world large-alphabet quantum-cryptography applications

Realization of a collective decoding of codeword states

This was also extended from the previous article quant-ph/9705043, especially in a realization of the decoding process.Comment: 6 pages, RevTeX, 4 figures(EPS

Performance of FEC codes over AWGN channel for efficient use in Polymer Optical Fiber links

Volume 1 Issue 7 (September 2013