Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Research in Optical Sciences

Time emerging from quantum correlations

Ekaterina V. Moreva, G. Brida, Marco Gramegna, Vittorio Giovannetti, Lorenzo Maccone, Marco Genovese

Published Jan 1, 2014• 0 citations
Publisher

Abstract

Page and Wootters’ mechanism of “static” time is experimentally realized using a static, entangled state of the polarization of two photons, one of which serves as a clock to gauge the evolution of the second.
DOI
10.1364/qim.2014.qtu1a.2

Related papers

Entanglement discloses Time as an emergent phenomenon

Ekaterina V. Moreva, G. Brida, Marco Gramegna +3 more

Page and Wootters’ mechanism of “static” time is experimentally implemented by a toy universe consisting of a polarization entangled photon pair, one of which serves as a clock to gauge the evolution of the second.

•Jan 1, 2014•3 citations

Time from quantum entanglement: An experimental illustration

Ekaterina V. Moreva, G. Brida, Marco Gramegna +3 more

In previous years several theoretical papers discussed if time can be an emergent property deriving from quantum correlations. Here, to provide insight into how this phenomenon can occur, we present an experiment that illustrates Page and Wootters' mechanism of ``static'' time [D. N. Page and W. K. Wootters, Phys. Rev. D 27, 2885 (1983)], and Gambini et al. for subsequent refinements [R. Gambini et al., Phys. Rev. D 79, 041501(R) (2009)]. A static, entangled state between a clock system and the rest of the universe is perceived as evolving by internal observers that test the correlations between the two subsystems. We implement this mechanism using an entangled state of the polarization of two photons, one of which is used as a clock to gauge the evolution of the second: An ``internal'' observer that becomes correlated with the clock photon sees the other system evolve, while an ``external'' observer that only observes global properties of the two photons can prove it is static.

arXiv:1310.4691•Physical Review A•May 20, 2014•133 citations

The time as an emergent property of quantum mechanics, a synthetic description of a first experimental approach

Ekaterina V. Moreva, G. Brida, Marco Gramegna +3 more

The ''problem of time" in present physics substantially consists in the fact that a straightforward quantization of the general relativistic evolution equation and constraints generates for the Universe wave function the Wheeler-De Witt equation, which describes a static Universe. Page and Wootters considered the fact that there exist states of a system composed by entangled subsystems that are stationary, but one can interpret the component subsystems as evolving: this leads them to suppose that the global state of the universe can be envisaged as one of this static entangled state, whereas the state of the subsystems can evolve. Here we synthetically present an experiment, based on PDC polarization entangled photons, that shows a practical example where this idea works, i.e. a subsystem of an entangled state works as a 'clock" of another subsystem.

arXiv:1502.03264•Journal of Physics Conference Series•Jul 3, 2015•4 citations

Self-measurement of the quantum universe leads to emergence of time

Michael B. Mensky

Physics Letters A•Jun 1, 1990•9 citations

Quantum Time as an Observable: Basis-Dependent Dynamics and an Experimental Test

Daniil Domekin

•Apr 2, 2026•0 citations

Robustness of the Page-Wootters construction across different pictures, states of the universe, and system-clock interactions

Simone Rijavec

In quantum theory, the concept of time rests on shaky ground. One way to address this problem is to remove the usual background time parameter as a primitive entity and explain its emergence via correlations between physical systems. This approach was adopted by Page and Wootters [Phys. Rev. D 27, 2885 (1983)], who showed how time can emerge in a stationary quantum universe from the correlations between two of its subsystems, one of them acting as a clock for the other. In this work, I study the robustness of the Page-Wootters construction across different pictures, states of the universe, and clock interactions, clarifying the role and the nature of the correlations between the subsystems of the universe. I start by showing how to formulate the Page-Wootters construction in the Heisenberg picture via a unitary change of basis. I consider both pure and mixed states of the universe and extend the analysis to include interactions between the clock and the other subsystem of the universe. The study reveals what kind of correlations are necessary for the construction to work. Interestingly, entanglement is not required as long as there are no interactions with the clock. The study also shows that these interactions can lead to a nonunitary evolution for some mixed states of the universe. In a simple two-level system, this aspect becomes relevant at scales where one would expect strong relativistic effects. At these scales, I also observe an inversion in the system's direction of time.

arXiv:2204.11740•Physical review. D/Physical review. D.•Sep 11, 2023•9 citations
In previous years several theoretical papers discussed if time can be an emergent property deriving from quantum correlations. Here, to provide insight into how this phenomenon can occur, we present an experiment that illustrates Page and Wootters' mechanism of ``static'' time [D. N. Page and W. K. Wootters, Phys. Rev. D 27, 2885 (1983)], and Gambini et al. for subsequent refinements [R. Gambini et al., Phys. Rev. D 79, 041501(R) (2009)]. A static, entangled state between a clock system and the rest of the universe is perceived as evolving by internal observers that test the correlations between the two subsystems. We implement this mechanism using an entangled state of the polarization of two photons, one of which is used as a clock to gauge the evolution of the second: An ``internal'' observer that becomes correlated with the clock photon sees the other system evolve, while an ``external'' observer that only observes global properties of the two photons can prove it is static.
The ''problem of time" in present physics substantially consists in the fact that a straightforward quantization of the general relativistic evolution equation and constraints generates for the Universe wave function the Wheeler-De Witt equation, which describes a static Universe. Page and Wootters considered the fact that there exist states of a system composed by entangled subsystems that are stationary, but one can interpret the component subsystems as evolving: this leads them to suppose that the global state of the universe can be envisaged as one of this static entangled state, whereas the state of the subsystems can evolve. Here we synthetically present an experiment, based on PDC polarization entangled photons, that shows a practical example where this idea works, i.e. a subsystem of an entangled state works as a 'clock" of another subsystem.
In quantum theory, the concept of time rests on shaky ground. One way to address this problem is to remove the usual background time parameter as a primitive entity and explain its emergence via correlations between physical systems. This approach was adopted by Page and Wootters [Phys. Rev. D 27, 2885 (1983)], who showed how time can emerge in a stationary quantum universe from the correlations between two of its subsystems, one of them acting as a clock for the other. In this work, I study the robustness of the Page-Wootters construction across different pictures, states of the universe, and clock interactions, clarifying the role and the nature of the correlations between the subsystems of the universe. I start by showing how to formulate the Page-Wootters construction in the Heisenberg picture via a unitary change of basis. I consider both pure and mixed states of the universe and extend the analysis to include interactions between the clock and the other subsystem of the universe. The study reveals what kind of correlations are necessary for the construction to work. Interestingly, entanglement is not required as long as there are no interactions with the clock. The study also shows that these interactions can lead to a nonunitary evolution for some mixed states of the universe. In a simple two-level system, this aspect becomes relevant at scales where one would expect strong relativistic effects. At these scales, I also observe an inversion in the system's direction of time.