
Physics Letters B 795 (2019) 183–187
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Spectral form factor as an OTOC averaged over the Heisenberg group
Robert de Mello Koch
a,b
, Jia-Hui Huang
b,∗
, Chen-Te Ma
b,c
, Hendrik J.R. Van Zyl
b
a
Institute of Quantum Matter, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006, Guangdong, China
b
School of Physics and Mandelstam Institute for Theoretical Physics, University of Witwatersrand, Wits 2050, South Africa
c
The Laboratory for Quantum Gravity and Strings, Department of Mathematics and Applied Mathematics, University of Cape Town, Private Bag,
Rondebosch 7700, South Africa
a r t i c l e i n f o a b s t r a c t
Article history:
Received
1 June 2019
Accepted
12 June 2019
Available
online 17 June 2019
Editor:
N. Lambert
Keywords:
Spectral
form factor
Out-of-time
ordered correlation function
Heisenberg
group
Late-time
limit
We prove that in bosonic quantum mechanics the two-point spectral form factor can be obtained as
an average of the two-point out-of-time ordered correlation function, with the average taken over
the Heisenberg group. In quantum field theory, there is an analogous result with the average taken
over the tensor product of many copies of the Heisenberg group, one copy for each field mode. The
resulting formula is expressed as a path integral over two fields, providing a promising approach to the
computation of the spectral form factor. We develop the formula that we have obtained using a coherent
state description from the JC model and also in the context of the large-N limit of CFT and Yang-Mills
theory from the large-N matrix quantum mechanics.
© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
Many-body quantum chaos [1]plays an important role in the
strong coupling dynamics of systems in many fields of physics,
including condensed matter physics, quantum information theory,
and quantum gravity. Although one cannot rely on the character-
istic
exponential sensitivity to initial conditions when considering
unitary quantum evolution (see for example [2]), quantum chaotic
systems share common features.
Two
main criteria used to decide if a system exhibits quan-
tum
chaos or not, are the spectral form factor (SFF) [3] and the
out-of-time ordered correlation function (OTOC) [4]. These probe
the irregular dynamics and sensitivity to the initial conditions re-
spectively.
The motivation for the SFF is rooted in random matrix
theory [5]. It is conjectured that a generic quantized system with a
classical chaotic limit should exhibit the spectral statistics of a ran-
dom
matrix ensemble. A concrete realization of this conjecture is
that of Sinai’s billiard [6–8]. A more recent related proposal iden-
tifies
the late time behavior of certain strongly coupled theories
(including the Sachdev-Ye-Kitaev (SYK) model) [9,10]with a large
number of degrees of freedom, captured in the two-point SFF
*
Corresponding author.
E-mail
addresses: robert@neo.phys.wits.ac.za (R. de Mello Koch),
huangjh@m.scnu.edu.cn (J.-H. Huang), yefgst@gmail.com (C.-T. Ma),
hjrvanzyl@gmail.com (H.J.R. Van Zyl).
g
2
(β, t) ≡
R
2
(β, t)
R
2
(0, t)
;
R
2
(β, t) ≡|Tr
(
exp(−β H −iHt)
)
|
2
(1)
with a dynamical form of random matrix universality [11]. In the
above β is the inverse temperature and H is the Hamiltonian of
the system.
In
contrast to the SFF, the OTOC probes chaos at early time [4,
12].
This should be due to the quantum uncertainty relation or
losing infinitesimal perturbation in a local quantum system [2]. In
chaotic systems, the OTOC exhibits exponential decay with rate λ
and converges to a persistent small value. A semiclassical analysis
shows that the rate λ is naturally related to a Lyapunov exponent
[4]. Under some natural assumptions, it is possible to prove the
bound λ ≤ 2π /β in the regularized OTOC [13], revealing that λ is
an interesting quantity for theoretical considerations. Note that it
has been shown that the unregularized OTOC does not share the
universal Lyapunov exponent with the regularized OTOC due to the
sensitivity of the infrared regulator [14–23]. Further, protocols to
measure the regularized OTOC have been given [24–26], applied
to Jaynes-Cummings (JC) interactions [27,28] and the Loschmidt
echo [29,30], and implemented [31,32] which confirms that λ is
an experimental observable. Taken together, these facts establish
the OTOC as a useful probe of quantum chaos.
Recently,
the saturation of the OTOC at late times has been
studied by connecting to spectral statistics through the correlation
functions [2]. This motivates the central question that we would
like to address in this letter: What is the relation between the spec-
tral
statistics and OTOC? This question is key to relating the early
and late time quantum behavior of a chaotic system. An important
https://doi.org/10.1016/j.physletb.2019.06.025
0370-2693/
© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.