UC Berkeley

We present the results of an experiment that used the quantized motion of an ion trappedin a harmonic pseudopotential to test for nonlinear extensions of quantum mechanics. This test was motivated by the development of a recent, consistent theory of nonlinear quantum mechanics that, in contrast to previous frameworks, also preserves causality. This experiment represents the first test of this new theory in a fully quantum system and improved the bounds on potential nonlinear effects in quantum mechanics inferred from previous experimental results by an estimated eight orders of magnitude.

We also present the results of an experiment that used two entangled ions to test for localviolations of Lorentz invariance and which tightened the bound on such hypothetical violations by about half of an order of magnitude. In particular, this experiment used a special entangled state of the ions, residing within a decoherence free subspace, which is immune to the dominant source of noise. By comparing our results against a similar experiment, performed with two non-entangled ions, we verify the expected factor-of-two improvement in the signal-to-noise ratio predicted by theory. This improvement can be directly attributed to the use of entanglement and, thus, this work provides a case study of how entanglement can be leveraged as a resource to fundamentally enhance the performance of spectroscopic measurements