Time from quantum entanglement: an experimental illustration (1310.4691v1)

Abstract: In the last years several theoretical papers discussed if time can be an emergent property deriving from quantum correlations. Here, to provide an insight into how this phenomenon can occur, we present an experiment that illustrates Page and Wootters' mechanism of "static" time, and Gambini et al. subsequent refinements. 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 paper demonstrates that time emerges from entangled photon states by employing the Page-Wootters mechanism in a clock-system experimental setup.
• The experiment reveals that internal observers perceive time evolution while external observers detect a static global state using dual observation modes.
• The study validates theoretical models by matching conditional probabilities from quantum correlations with predictions and addressing criticisms of the Page-Wootters framework.

Analyzing Time Emergence via Quantum Entanglement

The paper "Time from quantum entanglement: an experimental illustration" by Moreva et al. provides an intriguing exploration of the concept of time emergent from quantum correlations, based on Page and Wootters' mechanism (PaW) and further refinements by Gambini et al. This investigation probes whether the flow of time, as perceived by internal observers, originates from the entangled state of quantum systems, conflicting with the notion of a universal static state suggested by the Wheeler-DeWitt equation.

Core Experiment

The authors put forth an experimental realization using the entanglement of two photon polarizations. Within this framework, one photon acts as a "clock," while the other constitutes the system under observation. They ingeniously implement the PaW mechanism that hypothesizes a perspective where an observer internal to the universe perceives subsystems in evolution, while an external observer perceives the universe as static when considering global properties.

• Observer Mode: Internal observers made use of the photons' polarizations to detect time evolution. They measured the time-dependent polarization states using a simple setup where time is indicated by the polarization of the clock photon.
• Super-Observer Mode: By using a quantum erasure technique, external observers demonstrate that global state remains static, consistent with the Wheeler-DeWitt equation that suggests a static universe.

Theoretical Implications and Numerical Results

The results suggest that even using a simple two-level clock system, internal observers can perceive an evolving state, which implies that time may indeed emerge from quantum correlations in subsystems of the universe. When photons' polarization served as clock readings, the conditional probabilities extracted matched theoretical expectations, demonstrating that such a system could simulate evolution within the PaW model framework. The fidelity of the observed states supports the notion of a static global entangled state when analyzed from an external viewpoint.

Addressing Concerns and Extending the Model

Two major criticisms of the PaW model include the improbability of quantum mechanics describing the universe's totality, and difficulties in deriving concrete transition probabilities and propagators. This research addresses these by experimenting under the assumptions of non-interacting subsystems and by utilizing the subsequent refinements suggested by Gambini et al., extending the model to accommodate evolving constants.

The explorations of the GPPT extension focused on multiple time measurements, seeking to average over abstract coordinate time, which is typically inaccessible. The resulting probabilities mirrored theoretical constructs, portraying an evolving subsystem with a reduced need for explicating external time, aligning with the proposed theoretical mechanisms.

Future Prospects and Considerations

The ramifications of this experiment touch upon profound issues in quantum mechanics and quantum gravity, specifically regarding the interpretation and measurement of time. Further developments could enhance understanding in areas such as quantum cosmology and time perception in quantum systems.

Future research directions may incorporate larger, more complex systems, aiming for higher-precision quantum clocks, and investigating how these mechanisms scale with increasingly complicated systems. Additionally, the combination of theoretical insight and experimental validation may prompt refinements in existing models or propose new frameworks consistent with quantum theory while addressing time perception.

Thus, the paper enriches the discourse on quantum time, posing thought-provoking questions about our understanding of time within quantum mechanics and offering empirical affirmation of theoretical constructs regarding time's emergence from quantum entanglement.