  The homodyne detection is one of the most basic tools for identifying the
quantum state of light. It has been used to detect useful non-local properties,
such as entanglement for the quantum teleportation and distillability of a
secret key in quantum key distribution. In so doing, the detection scheme
employs a bright optical pulse, called the local oscillator (LO) pulse, and the
LO pulse is usually transmitted along with the signal pulses. The LO pulse is
presumed to be a coherent state with an infinite intensity. However, it is
difficult in practice to hold this presumption owing to noise in the optical
transmission channels or an intervention by a malicious third party. As a
result, the implementation may no longer be the homodyne detection, and those
outcomes may merely disguise successful detection of entanglement or a secret
key. Here, we present an alternative scheme that works as the homodyne
detection to detect the non-local properties of light in a verifiable manner,
without any presumption for the LO pulses. This scheme is essentially based on
the same setup as the conventional implementation for the homodyne detection.
This result contributes to close any possible loophole in the homodyne
detection caused by the deviation from the ideal LO pulses.
