Tunneling spectroscopy of a macroscopic variable

We develop a theory of the line shape for macroscopic tunneling spectroscopy and show how both spectral linewidths and line shifts are related to phenomenological dissipative coefficients for the relevant macroscopic coordinate. In the limit of weak dissipation our theory justifies a simple approximate interpretation of recent experiments on Josephson junctions; in this way macroscopic tunneling spectroscopy can be used to obtain accurate in situ estimates of the parameters required to calculate the absolute rate of macroscopic tunneling. Our calculations also clarify the extent to which spectroscopic experiments provide evidence for macroscopic quantum behavior.