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Published March 1, 2017 | Submitted
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Quantum Circuit Cosmology: The Expansion of the Universe Since the First Qubit


We consider cosmological evolution from the perspective of quantum information. We present a quantum circuit model for the expansion of a comoving region of space, in which initially-unentangled ancilla qubits become entangled as expansion proceeds. We apply this model to the comoving region that now coincides with our Hubble volume, taking the number of entangled degrees of freedom in this region to be proportional to the de Sitter entropy. The quantum circuit model is applicable for at most 140 e-folds of inflationary and post-inflationary expansion: we argue that no geometric description was possible before the time t_1 when our comoving region was one Planck length across, and contained one pair of entangled degrees of freedom. This approach could provide a framework for modeling the initial state of inflationary perturbations.

Additional Information

N. B. would like to acknowledge Sabrina Pasterski and Stephen Jordan for comments on the draft. L. M. is indebted to Tom Hartman for extensive explanations, and to Thomas Bachlechner, Sandipan Kundu, and John Stout for helpful discussions and comments on a draft. L. M. thanks the Caltech theory group for their hospitality during the initial stages of this work. C. C. and S. C. would like to thank Aidan Chatwin-Davies for detailed comments and discussions on the draft. This research is funded in part by the Walter Burke Institute for Theoretical Physics at Caltech, by DOE grant DE-SC0011632, by the Foundational Questions Institute, by the Gordon and Betty Moore Foundation through Grant 776 to the Caltech Moore Center for Theoretical Cosmology and Physics, and by NSF grant PHY-131622.

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