A discrete quantum process is represented by a sequence of quantum operations, which are completely positive maps that are not necessarily trace preserving. We consider quantum processes that are obtained by repeated iterations of a quantum operation with noise. Such ergodic quantum processes generalize independent quantum processes. An ergodic theorem describing convergence to equilibrium for a general class of such processes has been recently obtained by Movassagh and Schenker. Under irreducibility and mixing conditions, we obtain a central limit type theorem describing fluctuations around the ergodic limit.

1.
Billingsley
,
P.
, “
The Lindeberg-Lévy theorem for martingales
,”
Proc. Am. Math. Soc.
12
(
5
),
788
792
(
1961
).
2.
Billingsley
,
P.
,
Probability and Measure
(
John Wiley & Sons
,
2008
).
3.
Birkhoff
,
G. D.
, “
Proof of the ergodic theorem
,”
Proc. Natl. Acad. Sci. U. S. A.
17
(
12
),
656
660
(
1931
).
4.
Brown
,
B. M.
, “
Martingale central limit theorems
,”
Ann. Math. Stat.
42
,
59
66
(
1971
).
5.
Cohn
,
H.
,
Nerman
,
O.
, and
Peligrad
,
M.
, “
Weak ergodicity and products of random matrices
,”
J. Theor. Probab.
6
(
2
),
389
405
(
1993
).
6.
Conze
,
J.-P.
and
Raugi
,
A.
, “
Limit theorems for sequential expanding dynamical systems
,” in
Ergodic Theory and Related Fields: 2004–2006 Chapel Hill Workshops on Probability and Ergodic Theory
(
University of North Carolina; American Mathematical Society
,
Chapel Hill, NC
,
2007
), Vol.
430
, p.
89
.
7.
Cornfeld
,
I. P.
,
Fomin
,
S. V.
, and
Sinai
,
Y. G.
,
Ergodic Theory
(
Springer Science & Business Media
,
2012
), Vol.
245
.
8.
Doukhan
,
P.
,
Mixing: Properties and Examples
(
Springer Science & Business Media
,
2012
), Vol.
85
.
9.
Dürr
,
D.
and
Goldstein
,
S.
, “
Remarks on the central limit theorem for weakly dependent random variables
,” in
Stochastic Processes—Mathematics and Physics
(
Springer
,
1986
), pp.
104
118
.
10.
Evans
,
D. E.
and
Høegh-Krohn
,
R.
, “
Spectral properties of positive maps on C*-algebras
,”
J. London Math. Soc.
s2–17
(
2
),
345
355
(
1978
).
11.
Furstenberg
,
H.
and
Kesten
,
H.
, “
Products of random matrices
,”
Ann. Math. Stat.
31
(
2
),
457
469
(
1960
).
12.
Gol’dsheid
,
I. Y.
and
Margulis
,
G. A.
, “
Lyapunov indices of a product of random matrices
,”
Russ. Math. Surv.
44
(
5
),
11
71
(
1989
).
13.
Gordin
,
M. I.
, “
The central limit theorem for stationary processes
,”
Sov. Math. Dokl.
10
,
1174
1176
(
1969
).
14.
Hennion
,
H.
, “
Limit theorems for products of positive random matrices
,”
Ann. Probab.
25
,
1545
1587
(
1997
).
15.
Ibragimov
,
I. A.
, “
A central limit theorem for one class of dependent random variables
,”
Theor. Probab. Appl.
8
(
1
),
89
94
(
1963
)
16.
Kingman
,
J. F.
, “
Subadditive processes
,” in
Ecole d’Eté de Probabilités de Saint-Flour V-1975
(
Springer
,
1976
), pp.
167
223
.
17.
Kingman
,
J. F. C.
et al, “
Subadditive ergodic theory
,”
Ann. Probab.
1
(
6
),
883
899
(
1973
).
18.
Krein
,
M. G.
and
Rutman
,
M. A.
, “
Linear operators leaving invariant a cone in a Banach space
,”
Am. Math. Soc. Transl.
1950
(
26
),
128
.
19.
Liggett
,
T. M.
, “
An improved subadditive ergodic theorem
,”
Ann. Probab.
13
(
4
),
1279
1285
(
1985
).
20.
Liverani
,
C.
, “
Central limit theorem for deterministic systems
,” in
International Conference on Dynamical Systems, Montevideo, 1995, Pitman Research Notes in Mathematics Series 1995
(
1996
), Vol. 362, pp.
56
75
.
21.
Movassagh
,
R.
and
Schenker
,
J.
, “
Theory of ergodic quantum processes
,”
Phys. Rev. X
11
(
4
),
041001
(
2021
).
22.
Movassagh
,
R.
and
Schenker
,
J.
, “
An ergodic theorem for quantum processes with applications to matrix product states
,”
Commun. Math. Phys.
395
,
1175
(
2022
).
23.
Oseledec
,
V.
, “
A multiplicative ergodic theorem: Characteristic Lyapnov exponents of dynamical systems
,”
Trans. Moscow Math. Soc.
,
19
,
197
231
(
1968
).
24.
Walters
,
P.
,
An Introduction to Ergodic Theory
(
Springer Science & Business Media
,
2000
), Vol.
79
.
25.

Equivalently, no hereditary sub-algebra, PMDP with P being an orthogonal projection, is invariant under ϕ. See Ref. 10.

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