Sabine Wollmann

Observation of Genuine One-Way Einstein-Podolsky-Rosen Steering.

Within the hierarchy of inseparable quantum correlations, Einstein-Podolsky-Rosen steering is distinguished from both entanglement and Bell nonlocality by its asymmetry-there exist conditions where the steering phenomenon changes from being observable to not observable, simply by exchanging the role of the two measuring parties. While this one-way steering feature has been previously demonstrated for the restricted class of Gaussian measurements, for the general case of positive-operator-valued measures even its theoretical existence has only recently been settled. Here, we prove, and then experimentally observe, the one-way steerability of an experimentally practical class of entangled states in this general setting. As well as its foundational significance, the demonstration of fundamentally asymmetric nonlocality also has practical implications for the distribution of the trust in quantum communication networks.

Heralded quantum steering over a high-loss channel

Entanglement swapping enables verified nonlocal correlations over a high-loss channel with the detection loophole closed. Entanglement is the key resource for many long-range quantum information tasks, including secure communication and fundamental tests of quantum physics. These tasks require robust verification of shared entanglement, but performing it over long distances is presently technologically intractable because the loss through an optical fiber or free-space channel opens up a detection loophole. We design and experimentally demonstrate a scheme that verifies entanglement in the presence of at least 14.8 ± 0.1 dB of added loss, equivalent to approximately 80 km of telecommunication fiber. Our protocol relies on entanglement swapping to herald the presence of a photon after the lossy channel, enabling event-ready implementation of quantum steering. This result overcomes the key barrier in device-independent communication under realistic high-loss scenarios and in the realization of a quantum repeater.

Ultrasonically assisted deposition of colloidal crystals

Colloidal particles are a versatile physical system which have found uses across a range of applications such as the simulation of crystal kinetics, etch masks for fabrication, and the formation of photonic band-gap structures. Utilization of colloidal particles often requires a means to produce highly ordered, periodic structures. One approach is the use of surface acoustic waves (SAWs) to direct the self-assembly of colloidal particles. Previous demonstrations using standing SAWs were shown to be limited in terms of crystal size and dimensionality. Here, we report a technique to improve the spatial alignment of colloidal particles using traveling SAWs. Through control of the radio frequency power, which drives the SAW, we demonstrate enhanced quality and dimensionality of the crystal growth. We show that this technique can be applied to a range of particle sizes in the μm-regime and may hold potential for particles in the sub-μm-regime.

Strong Unitary and Overlap Uncertainty Relations: Theory and Experiment

We derive and experimentally investigate a strong uncertainty relation valid for any n unitary operators, which implies the standard uncertainty relation and others as special cases, and which can be written in terms of geometric phases. It is saturated by every pure state of any n-dimensional quantum system, generates a tight overlap uncertainty relation for the transition probabilities of any n+1 pure states, and gives an upper bound for the out-of-time-order correlation function. We test these uncertainty relations experimentally for photonic polarization qubits, including the minimum uncertainty states of the overlap uncertainty relation, via interferometric measurements of generalized geometric phases.