RAMBOQ P R obabilistic g A tes M aking B inary O ptical Q uanta Contract no.: IST-2001-38864

1. RAMBOQPRobabilistic gAtes Making Binary Optical QuantaContract no.: IST-2001-38864 Coordinator: J.G. Rarity

2. Abstract We will explore the possibility of building scalable quantum information processors using novel ideas of linear quantum logic. This will include probabilistic CNOT gates assembled from single photon sources and sources of entangled states. We will also investigate the development of higher dimensional quantum logic aimed at developing error resilient quantum networks. Supporting work will develop more efficient detectors and practical single and multi-photon sources suitable for logic realisations. A theoretical effort will aim to increase the efficiency of simple gates and look a scalability, error correction and the overall limits to this technology.

3. Objectives • RAMBOQ seeks to develop scalable quantum processors • Robust optical links between quantum processors. • Efficient quantum computation using conditional linear logic. • Evaluate theoretical limits to conditional linear logic • Reduce gate complexity and increase efficiency. • Efficient creation of single photon input states, single mode entangled states and efficient read out detectors. • Single gate to cascaded (few gate) quantum logic. • Novel quantum communication schemes: sharing/teleportation of quantum states • Novel logic schemes using higher order states for multi-party quantum protocols.

4. Simplified Workplan six monthly meetings in WP0 feed through of theoretical support throughout the programme, feed out of sources and detectors to to WP3-5 during months 18-27 feed simple gate concepts to WP4/5 during months 12-24, feed near term application ideas to WP6 in months 22-30. 2003 2004 2005 WP0 Management WP1 Theory of linear quantum logic WP2 Input-output: Single/pair Photon Sources and Detectors WP3 Implementation of quantum logic. WP4 Tools for Quantum Networks WP5 Higher dimensional Hilbert spaces WP6 Applications

5. Partners

6. Original KLM gate, based on 2-mode interferometers.

7. A compact twin photon source pump L R • Key features: • narrow spectral width • generation of entangled pairs of photons • coupling into fibers

8. Main steps towards a twin photon source • Modelisation Losses measurements (University Paris 7) • Growth and processing (THALES) • Surface emitting SHG • and index measurements • (University of Rome) • Twin photon source charcaterisation • Quantum optics experiments (University of Geneva)

9. Cryostat Confocal microscope for study of single dot emitters

10. Single photon interference: characterisation of single photon source Requires a time bandwidth limited single photon source

11. Scalable gate? Using teleportation to make non-destructive gates Destructive CNOT

12. Higher order Hilbert Spaces Will also be implemented in time bin entanglement scheme

13. Entanglement Purification

14. Key deliverables • Simple experimentally achievable two qubit gate design M12 • Prototype single photon source displaying quantum interference M24 • Novel pair photon sources for Q Logic applications M24 • Demonstration of destructive CNOT function M12 • Demonstration of entanglement purification, long distance entanglement swapping and quantum telecloning M24 • Demonstration of Byzantine agreement and multiparty secret sharing M24 • Review of applications of linear quantum logic, quantum networking and higher Hilbert space encoding M36 • Report on experiments to demonstrate scalable and cascadable CNOT gates M36