The vacuum expectation values of the so-called Q-operators of certain integ
rable quantum field theories have recently been identified with spectral de
terminants of particular Schrodinger operators. In this paper we extend the
correspondence to the T-operators, finding that their vacuum expectation v
alues also have an interpretation as spectral determinants, As byproducts w
e give a simple proof of an earlier conjecture of ours, proved by another r
oute by Suzuki, and generalise a problem in PT symmetric quantum mechanics
studied by Bender and Boettcher. We also stress that the mapping between Q-
operators and Schrodinger equations means that certain problems in integrab
le quantum field theory are related to the study of Regge Doles in non-rela
tivistic potential scattering. (C) 1999 Elsevier Science B.V. All rights re
served.