Comment on "Quantum time crystals".

  title={Comment on "Quantum time crystals".},
  author={Patrick Bruno},
  journal={Physical review letters},
  volume={110 11},
  • P. Bruno
  • Published 15 October 2012
  • Physics
  • Physical review letters
A Comment on Frank Wilczek's paper "Quantum Time Crystals" (Phys. Rev. Lett. 109, 160401 (2012); arXiv:1202.2539). 

Comment on "Quantum Time Crystals and Interacting Gauge Theories in Atomic Bose-Einstein Condensates".

It is shown that the energy of the chiral soliton in the laboratory frame is not correctly calculated in the Letter and the correct energy becomes minimal if the soliton does not move.

Classes of metastable thermodynamic quantum time crystals

We found that thermodynamic quantum time crystals in fermi systems, defined as quantum orders oscillating periodically in the imaginary Matsubara time with zero mean, are metastable for two general

Absence of Quantum Time Crystals.

A no-go theorem is proved that rules out the possibility of time crystals defined as such, in the ground state or in the canonical ensemble of a general Hamiltonian, which consists of not-too-long-range interactions.

Lack of a genuine time crystal in a chiral soliton model

In a recent publication [Phys. Rev. Lett. {\bf 124}, 178902] Ohberg and Wright claim that in a chiral soliton model it is possible to realize a genuine time crystal which corresponds to a periodic

Boundary Time Crystals.

This work introduces boundary time crystals and analyzes in detail a solvable model where an accurate scaling analysis can be performed.

Isolated Heisenberg magnet as a quantum time crystal

Local observables of closed many-body quantum systems are generally believed to quickly equilibrate after a quench, according to the eigenstate thermalization hypothesis. Here, the authors show that

Quantum Time Crystals and Interacting Gauge Theories in Atomic Bose-Einstein Condensates.

This work studies the dynamics of a Bose-Einstein condensate trapped circumferentially on a ring, and shows that the associated density-dependent gauge potential and concomitant current nonlinearity permits a ground state in the form of a rotating chiral bright soliton.

Dynamical nonlocality in quantum time via modular operators

We formalize the concept of the modular energy operator within the Page and Wootters timeless framework. As a result, this operator is elevated to the same status as the more studied modular

Observation of a Space-Time Crystal in a Superfluid Quantum Gas.

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.

A dissipative time crystal with or without Z2 symmetry breaking

We study an emergent semiclassical time crystal composed of two interacting driven-dissipative bosonic modes. The system has a discrete Z2 spatial symmetry which, depending on the strength of the



The European Synchrotron Radiation Facility

  • S. Tazzari
  • Physics
    IEEE Transactions on Nuclear Science
  • 1985
A new design study for the European Synchrotron Radiation Facility (ESRF) has been carried out in the past year by the European Synchrotron Radiation Project Group. The aim was to extend the work

Wilczek's omission of the double-counting correction for the interaction energy in Ref