Physicists from the University of Amsterdam have proposed a new architecture
for a scalable quantum computer. Making use of the collective motion of the
constituent particles, they were able to construct new building blocks for
quantum computing that pose fewer technical difficulties than current
state-of-the art methods. The results were recently published in Physical
Review Letters.
The researchers work at QuSoft and the Institute of Physics in the groups of
Rene Gerritsma and Arghavan Safavi-Naini. The effort, which was led by the
Ph.D. candidate Matteo Mazzanti, combines two important ingredients. One is
a so-called trapped-ion platform, one of the most promising candidates for
quantum computing that makes use of ions—atoms that have either a surplus or
a shortage of electrons and as a result are electrically charged. The other
is the use of a clever method to control the ions supplied 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 more importantly, also as a
whole. As it turns out, the possible collective motions of the ions
facilitate the interactions between individual pairs of ions. In the
proposal, this idea is made concrete by applying a uniform electric field to
the whole crystal, in order to mediate interactions between two specific
ions in that crystal. The two ions are selected by applying tweezer
potentials on them—see the image above. The homogeneity of the electric
field assures that it will only allow the two ions to move together with all
other ions in the crystal. As a result, the interaction strength between the
two selected ions is fixed, regardless of how far apart the two ions are.
A quantum computer consists of 'gates,' small computational building blocks
that perform quantum analogs of operations like '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 setup, the fact that those interactions do not
depend on the distance means that also the duration of operation of a gate
is independent of that distance. As a result, this scheme for quantum
computing is inherently scalable, and compared to other state-of-the-art
quantum computing schemes poses fewer technical challenges for achieving
comparably well-operating quantum computers.
Reference:
M. Mazzanti et al, Trapped Ion Quantum Computing Using Optical Tweezers and
Electric Fields, Physical Review Letters (2021).
DOI: 10.1103/PhysRevLett.127.260502
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Physics