arXiv subjects

M. M. Donegan

Publications and source records attributed to M. M. Donegan.

3 recordsLinked to original sources

arXiv2003

Generation of entangled ancilla states for use in linear optics quantum computing

We describe several different methods for generating the entangled ancilla states that are required for linear optics quantum computing. We show that post-selection can be used in combination with linear optical elements to generate the entangled ancilla, but with an exponentially-small efficiency. Alternatively, the ancilla can be efficiently generated using solid-state devices consisting of quantum wells coupled with tunnel junctions. Finally, we consider the possibility of using encoded ancilla in order to reduce the effects of decoherence and measurement errors.

quant-ph↗

arXiv2003

Heralded Two-Photon Entanglement from Probabilistic Quantum Logic Operations on Multiple Parametric Down-Conversion Sources

An ideal controlled-NOT gate followed by projective measurements can be used to identify specific Bell states of its two input qubits. When the input qubits are each members of independent Bell states, these projective measurements can be used to swap the post-selected entanglement onto the remaining two qubits. Here we apply this strategy to produce heralded two-photon polarization entanglement using Bell states that originate from independent parametric down-conversion sources, and a particular probabilistic controlled-NOT gate that is constructed from linear optical elements. The resulting implementation is closely related to an earlier proposal by Sliwa and Banaszek [quant-ph/0207117], and can be intuitively understood in terms of familiar quantum information protocols. The possibility of producing a ``pseudo-demand'' source of two-photon entanglement by storing and releasing these heralded pairs from independent cyclical quantum memory devices is also discussed.

quant-ph↗

arXiv2002

High-fidelity quantum logic operations using linear optical elements

Knill, Laflamme, and Milburn [Nature 409, 46 (2001)] have shown that quantum logic operations can be performed using linear optical elements and additional ancilla photons. Their approach is probabilistic in the sense that the logic devices fail to produce an output with a failure rate that scales as 1/n, where n is the number of ancilla. Here we present an alternative approach in which the logic devices always produce an output with an intrinsic error rate that scales as 1/n^2,which may have several advantages in quantum computing applications.

quant-ph↗