  Continuous-variable (CV) measurement-device-independent (MDI) quantum key
distribution (QKD) is immune to imperfect detection devices, which can
eliminate all kinds of attacks on practical detectors. Here we first propose a
CV-MDI QKD scheme using unidimensional modulation (UD) in general
phase-sensitive channels. The UD CV-MDI QKD protocol is implemented with the
Gaussian modulation of a single quadrature of the coherent states prepared by
two legitimate senders, aiming to simplify the implementation compared with the
standard, symmetrically Gaussian-modulated CVMDI QKD protocol. Our scheme
reduces the complexity of the system since it ignores the requirement in one of
the quadrature modulations as well as the corresponding parameter estimations.
The security of our proposed scheme is analyzed against collective attacks, and
the finite-size analysis under realistic conditions is taken into account. UD
CV-MDI QKD shows a comparable performance to that of its symmetrical
counterpart, which will facilitate the simplification and practical
implementation of the CV-MDI QKD protocols.
