  As of today, no one can tell when a universal quantum computer with thousands
of logical quantum bits (qubits) will be built. At present, most quantum
computer prototypes involve less than ten individually controllable qubits, and
only exist in laboratories for the sake of either the great costs of devices or
professional maintenance requirements. Moreover, scientists believe that
quantum computers will never replace our daily, every-minute use of classical
computers, but would rather serve as a substantial addition to the classical
ones when tackling some particular problems. Due to the above two reasons,
cloud-based quantum computing is anticipated to be the most useful and
reachable form for public users to experience with the power of quantum. As
initial attempts, IBM Q has launched influential cloud services on a
superconducting quantum processor in 2016, but no other platforms has followed
up yet. Here, we report our new cloud quantum computing service -- NMRCloudQ
(http://nmrcloudq.com/zh-hans/), where nuclear magnetic resonance, one of the
pioneer platforms with mature techniques in experimental quantum computing,
plays as the role of implementing computing tasks. Our service provides a
comprehensive software environment preconfigured with a list of quantum
information processing packages, and aims to be freely accessible to either
amateurs that look forward to keeping pace with this quantum era or
professionals that are interested in carrying out real quantum computing
experiments in person. In our current version, four qubits are already usable
with in average 1.26% single-qubit gate error rate and 1.77% two-qubit
controlled-NOT gate error rate via randomized benchmaking tests. Improved
control precisions as well as a new seven-qubit processor are also in
preparation and will be available later.
