  Variational quantum algorithms (VQAs) have been considered to be useful
applications of noisy intermediate-scale quantum (NISQ) devices. Typically, in
the VQAs, a parametrized ansatz circuit is used to generate a trial wave
function, and the parameters are optimized to minimize a cost function. On the
other hand, blind quantum computing (BQC) has been studied in order to provide
the quantum algorithm with security by using cloud networks. A client with a
limited ability to perform quantum operations hopes to have access to a quantum
computer of a server, and BQC allows the client to use the server's computer
without leakage of the client's information (such as input, running quantum
algorithms, and output) to the server. However, BQC is designed for
fault-tolerant quantum computing, and this requires many ancillary qubits,
which may not be suitable for NISQ devices. Here, we propose an efficient way
to implement the NISQ computing with guaranteed security for the client. In our
architecture, only N+ 1 qubits are required, under an assumption that the form
of ansatzes is known to the server, where N denotes the necessary number of the
qubits in the original NISQ algorithms. The client only performs single-qubit
measurements on an ancillary qubit sent from the server, and the measurement
angles can specify the parameters for the ansatzes of the NISQ algorithms.
No-signaling principle guarantees that neither parameters chosen by the client
nor the outputs of the algorithm are leaked to the server. This work paves the
way for new applications of NISQ devices.
