Paper highlighted in Phys. Rev. B
The paper “Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems”, recently published in Physical Review B, was highlighted as an “Editors’ suggestion” of this issue. The work results from a collaboration between Mário G. Silveirinha, Hugo Terças (GoLP/IPFN), and Mauro Antezza.
Quantum electronic systems (for example, an atom) containing two degenerate ground states – in other words, two fundamental quantum states with equal energy – are expected to be invariant for two fundamental symmetries: the changing of the arrow of time (time-reversal symmetry) and the ability to initialize the clock at an arbitrary time instant (time-translation symmetry).
While this is true for an isolated quantum system, things change when interacting with an environment occurs. In their work, the authors show that an atom-like system containing two degenerate ground states violates both time-reversal and time-translation symmetries when in contact with the electromagnetic vacuum.
At the origin of such violations is the spin (i.e. the intrinsic angular momentum) of the electron, which provokes a tiny energy imbalance in the two original ground states. By 'tiny' they mean orders of magnitude smaller than the typical energy scales of the atomic transitions (on the PHz level), but sufficiently large when compared to electronics and photonics scales (on the GHz level).
Such a fascinating physical effect, which allows for a practical implementation of a time-crystal – a periodic motion of the fundamental state, as envisaged by Franck Wilczek in 2012 –, comes with a plethora of applications in nanophotonics, such as high-sensitivity magnetic field detectors and high-precision photonics clocks.
To know more:
M. G. Silveirinha, H. Terças, and M. Antezza, Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems. Phys. Rev. B 108, 235154 (2023).
