Physicists from the University of Amsterdam have proposed a new architecture for a scalable quantum computer. By using the collective motion of the constituent particles, they were able to construct new building blocks for quantum computing that are less technically difficult than current state-of-the-art methods. The results were recently published in Physical examination letters.
Researchers work at QuSoft and the Institute of Physics in the groups of Rene Gerritsma and Arghavan Safavi-Naini. The effort, led by doctoral student Matteo Mazzanti, combines two important ingredients. One is a so-called trapped ion platform, one of the most promising candidates for quantum computing that uses ions – atoms that have either a surplus or a lack of electrons and, therefore, are electrically charged. The other is the use of a clever method to control the ions delivered by optical tweezers and oscillating electric fields.
As the name suggests, trapped ion quantum computers use a crystal of trapped ions. These ions can move individually, but above all, also as a whole. It turns out that the possible collective motions of ions facilitate interactions between individual pairs of ions. In the proposal, this idea is realized by applying a uniform electric field to the whole crystal, in order to mediate the interactions between two specific ions in this crystal. The two ions are selected by applying tweezer potentials to them – see image above. The homogeneity of the electric field ensures that it will only allow the two ions to move with all the other ions in the crystal. Consequently, the force of interaction between the two selected ions is fixed, whatever the distance which separates the two ions.
A quantum computer consists of “gates”, small computer building blocks that perform quantum analogs of operations such as “and” and “or” that we know from ordinary computers. In trapped ion quantum computers, these gates act on the ions, and their operation depends on the interactions between these particles. In the above configuration, the fact that these interactions do not depend on distance means that the operating time of a gate is also independent of this distance. As a result, this quantum computing scheme is inherently scalable and, compared to other state-of-the-art quantum computing schemes, poses fewer technical challenges to obtain quantum computers that perform comparably.
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