Entanglement of solid-state qubits by measurement

We show that two identical solid-state qubits can be made fully entangled ~starting from a completely mixed state! with probability 1/4 just by measuring them with a detector, equally coupled to the qubits. This happens in the case of repeated strong ~projective! measurements as well as in a more realistic case of weak continuous measurement. In the latter case, the entangled state can be identified by a flat spectrum of the detector shot noise, while the nonentangled state ~probability 3/4! leads to a spectral peak at the Rabi frequency with the maximum peak-to-pedestal ratio of 32/3.