Quantum mechanics with complex time: a comment to the paper by Rajeev

藤井, 幸一

Jan Linderberg

Kazuyuki Fujii

In (quant-ph/0701141) Rajeev studied quantization of the damped simple harmonic oscillator and introduced a complex-valued Hamiltonian (which is normal). In this note we point out that the quantization is interpreted as a quantum mechanics with {\bf complex time}. We also present a problem on quantization of classical control systems.

Ali Ayan, O. Teoman Turgut

In this work we present two rigorous results on the nonrelativistic Lee model following a method proposed by Rajeev in an unpublished article (S. G. Rajeev, hep-th 9902025). Thus this short paper should be considered as a commentary on Rajeev. In the unpublished paper of Rajeev, the renormalization of the Hamiltonian is accomplished at the level of resolvents. We first establish that the renormalized resolvent of the interacting Hamiltonian indeed defines a unique closed densely defined operator acting on the free Fock space of bosons. Next we give a justification in the mean field approximation that the ground state energy is bounded from below and the system has a good thermodynamic limit by elaborating along the original arguments of Rajeev. Our arguments in two dimensions do not yield better bounds, but this could be due to the inadequacy of the method used. In both cases though the ground state energy is not significantly altered to give a nontrivial ground state energy per particle.

Juan Gonzalo Muga, A. Ruschhaupt, A Del Campo

S C Tiwari

In this comment on arXiv:2503.17307 (PRL, 136, 240202, 2026), a novel idea using flag states to transform complex state vector and operators to real ones is argued to effectively lead to a quantum mechanics that is complex in the disguised form of real. The claim that real-valued quantum mechanics cannot be falsified is conceptually flawed. A new criterion based on the geometric phases is suggested to compare real and complex versions of quantum mechanics.