
5
latter is controlled by the measurement strength in the
parent quantum measurement model, implying that the
ST is an MIPT in the semiclassical limit.
The use of stochastic Langevin dynamics might sug-
gest the absence of entanglement in the semicalssical
limit. However, this naive inference is not correct. The
semicalssical limit of entanglement needs to be taken
carefully65–67, where one first obtains an SK path integral
for entanglement entropy, e.g., second Rényi entropy68,
in the quantum model and then takes the semiclassical
limit. This results in effective dynamical equations for
entanglement69 different from Eq.(3). The latter only de-
scribes the effective dynamics of positions and momenta,
as typically done in semiclassical approximations70, and
is useful for capturing OTOC (4) in the semiclassical
limit. However, the the connection between the growth
of OTOC and entanglement has been shown in vari-
ous situations71–73. Hence the ST transition in OTOC
suggests an entanglement transition in the semiclassical
limit.
The study of the MIPT in the fully quantum limit of
our model will be an interesting future direction since
systems of interacting oscillators under continuous mea-
surements mimic many realistic open quantum systems.
MIPTs have already been shown to exist for continu-
ous weak measurements within more tractable quantum
dynamics, like for quantum circuits37,38, and noninter-
acting fermionic systems7. Moreover, there are several
works41–43 on the Bose-Hubbard model that show MIPT
in the presence of measurements. The oscillator model
in our work can be easily mapped to an interacting bo-
son model. Thus, quite generally, MIPT as a function of
measurement strength is expected to occur in our models
even in the fully quantum limit.
We acknowledge useful suggestions and comments by
Sriram Ramaswamy and Sitabhra Sinha, and discus-
sions with Subhro Bhattacharjee, Sthitadhi Roy, and Sri-
ram Ganeshan. S.B. acknowledges support from SERB
(Grant No CRG/2022/001062), DST, India and QuST,
DST, India.
∗sibaramr@iisc.ac.in;sumilan@iisc.ac.in
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