  Typically, the aim of quantum metrology is to sense target fields with high
precision utilizing quantum properties. Unlike the typical aim, in this paper,
we use quantum properties for adding a new functionality to quantum sensors.
More concretely, we propose a delegated quantum sensor (a client-server model)
with security inbuilt. Suppose that a client wants to measure some target
fields with high precision, but he/she does not have any high-precision sensor.
This leads the client to delegate the sensing to a remote server who possesses
a high-precision sensor. The client gives the server instructions about how to
control the sensor. The server lets the sensor interact with the target fields
in accordance with the instructions, and then sends the sensing measurement
results to the client. In this case, since the server knows the control process
and readout results of the sensor, the information of the target fields is
available not only for the client but also for the server. We show that, by
using an entanglement between the client and the server, an asymmetric
information gain is possible so that only the client can obtain the sufficient
information of the target fields. In our scheme, the server generates the
entanglement between a solid state system (that can interact with the target
fields) and a photon, and sends the photon to the client. On the other hand,
the client is required to possess linear optics elements only including wave
plates, polarizing beam splitters, and single-photon detectors. Our scheme is
feasible with the current technology, and our results pave the way for a novel
application of quantum metrology.
