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Content archived on 2024-05-24

Experimental realisation of quantum gates and development of scalable quantum computer schemes in rare-earth-ion-doped inorganic crystals


We aim to experimentally demonstrate 2 and 3 bit quantum gates in rare-earth-ion-doped inorganic crystals (RE crystals) and to develop materials and design architectures appropriate for scalable RE crystal quantum computers. The qubit interaction mechanism in the crystal is based on ion-ion interaction between the rare earth ions. In order to enhance the ion-ion interaction to create scalable systems specially designed crystals with a high concentration of ion pairs, trimers and clusters will be grown and characterised. Scalable architectures, e.g. based on ´registers´ consisting of a limited number of mutually interacting ions (as would be the case in e.g. a cluster) connected by communication channels will be investigated. In a presently running FET open assessment project, REQC hardware, we have been able to isolate a qubit and observed the ion-ion interaction which will be used to entangle qubits.

The overall objective is to show that rare-earth-ion-doped inorganic crystals (RE crystals) is a strong solid state candidate for quantum computing. The aim is to reach this objective by:
1. Demonstrating CONTROL-NOT and CONTROL-CONTROL-NOT gates in RE crystals. This work includes the development of techniques for adiabatic coherent population transfer of the ensembles of ions in the qubit for qubit preparation and control;
2. Demonstrating that RE crystal quantum computing can be scalable by:
a. Growing new crystal materials specially designed for quantum gate operations;
b. Developing schemes and architectures for RE crystal quantum computers using material parameters consistent with, or that could be achieved based on, the experimental results and the properties of the developed crystals.

Based on the ongoing REQC hardware FET assessment project the judgement is that it is in principle straightforward to demonstrate two or three bit quantum gates in certain rare-earth-ion-doped crystals (RE crystals). However, the RE crystals and RE crystal transitions that have been investigated so far would not readily yield a scalable quantum computer system. The work in the ESQUIRE project is therefore on one hand focussed on continuing where the REQC project ends and really demonstrate the quantum gates using the experience that has been obtained regarding optical pumping schemes to prepare the qubits and the detection techniques for observing ion-ion interaction. On the other hand it is also focussed on finding scalable materials and concepts. Scalability can be achieved in systems with stronger ion-ion interaction. One way to achieve this is to put the ions closer to each other. Presently the technique to grow crystals where all rare earth ions form pairs at specific sites is mastered. The aim is to identify and grow crystals with pair formation that can be suitable for two-bit quantum gate operations and to extend the work to crystals with trimer and cluster formation. Here it is important that ground state coherence times remain sufficiently long (in the millisecond regime) when ion-ion interaction is increased. In parallel, theoretical work on novel implementations of gate operations, and new quantum computer schemes and architectures for RE crystals will be developed. This work will help to identify the weak points in the system and may identify specific material properties or other issues that may be important to improve in the material research or experimental part of the program in order to obtain a scalable system.

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EU contribution
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221 00 LUND

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Participants (9)