# Absence of Quantum Time Crystals.

@article{Watanabe2015AbsenceOQ, title={Absence of Quantum Time Crystals.}, author={Haruki Watanabe and Masaki Oshikawa}, journal={Physical review letters}, year={2015}, volume={114 25}, pages={ 251603 } }

In analogy with crystalline solids around us, Wilczek recently proposed the idea of "time crystals" as phases that spontaneously break the continuous time translation into a discrete subgroup. The proposal stimulated further studies and vigorous debates whether it can be realized in a physical system. However, a precise definition of the time crystal is needed to resolve the issue. Here we first present a definition of time crystals based on the time-dependent correlation functions of the order…

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W hen a collection of atoms reaches a sufficiently low temperature, they arrange themselves periodically in space to form a crystal. Since the equations that describe the atoms’ motion do not contain…

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This study proposes a form of a Hamiltonian for which the unitary dynamics exhibits the time crystalline behavior and breaks continuous TTS, based on a spin-1/2 many-body Hamiltonian which has long-range multispin interactions in the form of spin strings, thus bypassing previously known no-go theorems.

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The experimental observation of a discrete time crystal, in an interacting spin chain of trapped atomic ions, is presented, which opens the door to the study of systems with long-range spatio-temporal correlations and novel phases of matter that emerge under intrinsically non-equilibrium conditions.

Reply to "Comment on "Quantum Time Crystals from Hamiltonians with Long-Range Interactions""

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- 2020

In the note by Khemani et al. [arXiv:2001.11037] the authors express conceptual disagreement with our recent paper on quantum time crystals [Phys. Rev. Lett. 123, 210602]. They criticise the…

Comment on "Quantum Time Crystals from Hamiltonians with Long-Range Interactions"

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In a recent paper (Phys. Rev. Lett. 123, 210602), Kozin and Kyriienko claim to realize "genuine" ground state time crystals by studying models with long-ranged and infinite-body interactions. Here we…

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The observation of a space-time crystal using ultracold atoms, where the periodic structure in both space and time is directly visible in the experimental images, paving the way for the usage of space- time crystals for the discovery of novel nonequilibrium phases of matter.

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