  Within the last decade much progress has been made in the experimental
realisation of quantum computing hardware based on a variety of physical
systems. Rapid progress has been fuelled by the conviction that sufficiently
powerful quantum machines will herald enormous computational advantages in many
fields, including chemical research. A quantum computer capable of simulating
the electronic structures of complex molecules would be a game changer for the
design of new drugs and materials. Given the potential implications of this
technology, there is a need within the chemistry community to keep abreast with
the latest developments as well as becoming involved in experimentation with
quantum prototypes. To facilitate this, here we review the types of quantum
computing hardware that have been made available to the public through cloud
services. We focus on three architectures, namely superconductors, trapped ions
and semiconductors. For each one we summarise the basic physical operations,
requirements and performance. We discuss to what extent each system has been
used for molecular chemistry problems and highlight the most pressing hardware
issues to be solved for a chemistry-relevant quantum advantage to eventually
emerge.
