All evidence so far suggests that the absolute spatial orientation of an experiment never affects its outcome. This is reflected in the standard model of particle physics by requiring all particles and fields to be invariant under Lorentz transformations. The best-known tests of this important cornerstone of physics are Michelson-Morley-type experiments verifying the isotropy of the speed of light. For matter, Hughes-Drever-type experiments test whether the kinetic energy of particles is independent of the direction of their velocity, that is, whether their dispersion relations are isotropic. To provide more guidance for physics beyond the standard model, refined experimental verifications of Lorentz symmetry are desirable. Here we search for violation of Lorentz symmetry for electrons by performing an electronic analogue of a Michelson-Morley experiment. We split an electron wave packet bound inside a calcium ion into two parts with different orientations and recombine them after a time evolution of 95 milliseconds. As the Earth rotates, the absolute spatial orientation of the two parts of the wave packet changes, and anisotropies in the electron dispersion will modify the phase of the interference signal. To remove noise, we prepare a pair of calcium ions in a superposition of two decoherence-free states, thereby rejecting magnetic field fluctuations common to both ions. After a 23-hour measurement, we find a limit of h × 11 millihertz (h is Planck's constant) on the energy variations, verifying the isotropy of the electron's dispersion relation at the level of one part in 10(18), a 100-fold improvement on previous work. Alternatively, we can interpret our result as testing the rotational invariance of the Coulomb potential. Assuming that Lorentz symmetry holds for electrons and that the photon dispersion relation governs the Coulomb force, we obtain a fivefold-improved limit on anisotropies in the speed of light. Our result probes Lorentz symmetry violation at levels comparable to the ratio between the electroweak and Planck energy scales. Our experiment demonstrates the potential of quantum information techniques in the search for physics beyond the standard model.

We show that a chain of trapped ions embedded in microtraps generated by an optical lattice can be used to study oscillator models related to dry friction and energy transport. Numerical calculations with realistic experimental parameters demonstrate that both static and dynamic properties of the ion chain change significantly as the optical lattice power is varied. Finally, we lay out an experimental scheme to use the spin degree of freedom to probe the phase space structure and quantum critical behavior of the ion chain.

Lorentz symmetry is one of the cornerstones of modern physics. However, a number of theories aiming at unifying gravity with the other fundamental interactions including string field theory suggest violation of Lorentz symmetry [1][2][3][4]. While the energy scale of such strongly Lorentz symmetry-violating physics is much higher than that currently attainable by particle accelerators, Lorentz violation may nevertheless be detectable via precision measurements at low energies [2]. Here, we carry out a systematic theoretical investigation of the sensitivity of a wide range of atomic systems to violation of local Lorentz invariance (LLI). Aim of these studies is to identify which atom shows the biggest promise to detect violation of Lorentz symmetry. We identify the Yb + ion as an ideal system with high sensitivity as well as excellent experimental controllability. By applying quantum information inspired technology to Yb + , we expect tests of LLI violating physics in the electron-photon sector to reach levels of 10 −23 , five orders of magnitude more sensitive than the current best bounds [5][6][7]. Most importantly, the projected sensitivity of 10 −23 for the Yb + ion tests will allow for the first time to probe whether Lorentz violation is minimally suppressed at low energies for photons and electrons.Formally, we can classify LLI-violating effects in the framework of the Standard Model Extension (SME) [1]. The SME is an effective field theory that maintains Lorentz invariance of the total action, energy-momentum conservation, and gauge invariance, but supplements the Standard Model Lagrangian with all combinations of the SM fields that are not term-by-term Lorentz invariant. Here we focus on the c µν tensor term of the SME Lagrangian signifying the dependency of the maximally attainable velocity of a particle with respect to its propagation direction. SME allows for a violation of LLI for each type of particle, making it is essential to verify LLI in different systems at a high level of precision. As a result, LLI tests have been conducted for the photons [5], protons [8], neutrons [9,10], electrons [6,7], and neutrinos [11] with the detailed summary of all current limits given in [12].Testing LLI of the electron motion in a Coulomb potential created by a nucleus has the appeal of testing for new physics in a well understood system. In these atomic experiments [6,7], one searches for the variations of the atomic energy levels when the orientation of the electronic wave function is rotated with respect to the hypothetical preferred reference frame. The analysis of any experiment To analyze the atomic LLI experiments, we need to pick a reference frame which allows for two interpretations of the result: (a) we can either assume that the Coulomb potential is symmetric and any Lorentz-violating (LV) signal is attributed to the electron; or (b) we assume that electron obeys Lorentz symmetry and any LV signal is attributed to the photon sector.requires the selection of the preferred reference frame. In the present c...

Quantum correlations are at the heart of quantum information science 1-3 . Their detection usually requires access to all the correlated subsystems 4,5 . However, in many realistic scenarios this is not feasible, as only some of the subsystems can be controlled and measured. Such cases can be treated as open quantum systems interacting with an inaccessible environment 6 . Initial system-environment correlations play a fundamental role for the dynamics of open quantum systems 6-9 . Following a recent proposal 10,11 , we exploit the impact of the correlations on the open-system dynamics to detect system-environment quantum correlations without accessing the environment. We use two degrees of freedom of a trapped ion to model an open system and its environment. The present method does not require any assumptions about the environment, the interaction or the initial state, and therefore provides a versatile tool for the study of quantum systems.Quantum correlations are particularly important in the context of quantum simulation 12-14 , quantum phase transitions 15,16 , as well as for quantum computation 17 . In these experiments, one typically strives to study quantum many-body dynamics in high-dimensional Hilbert spaces. However, it is precisely in these complex systems where it becomes increasingly difficult to experimentally detect quantum correlations because standard methods such as full state tomography are impractical 18 . Therefore, it seems natural to restrict oneself to measurements of a smaller controllable subsystem 19 . Similarly, in quantum communication protocols, each party has access only to its part of the shared correlated state but may want to confirm the presence of quantum correlations locally 3 . All these situations can be described in the framework of a well-controlled open quantum system in contact with an inaccessible environment 6 .Initial system-environment correlations can significantly change the dynamics of open systems 6-9 . The standard master equation approach to open systems assumes an initial state with vanishing total correlations, which may not be appropriate unless a product state is explicitly prepared 20,21 . Moreover, the information flow between the system and its environment and the corresponding degree of non-Markovianity is closely related to the presence of correlations 9,22-24 .The present experiment follows a recently proposed protocol to detect nonclassical system-environment correlations of an arbitrary, unknown state by accessing only the open system 10,11 . The correlations are revealed through their effect on the open system dynamics. The protocol does not require any knowledge about the environment or the nature of the interaction, making it applicable to a wide range of scenarios where only partial access to a possibly correlated dynamical system is granted. the total system, which is connected to its accessible local subsystem in the grey box through the partial trace operation Tr E (dashed arrows). First, the accessible part ρ S of the unknown state ρ is me...