As recent disclosures have reminded us, security is not a simple matter. Most will tell you that the weak link in the chain is us: we simply don't use good security habits. But we're only one part of a number of issues. Although passwords are weaker than they should be, a strong password used on a weak system won't be much help. There is still a lot of necessary work being done to ensure that communication between parties is strongly encrypted.
One option that has received waves of attention over the last ten years is quantum key distribution (QKD). Despite its promise of absolute security, QKD has many practical difficulties that have limited it to niche applications. Now, in a nice bit of work, researchers have shown how to implement QKD for handheld devices.
A quick recap of QKD
Light has a property called polarization, which is measured with respect to a reference frame. So, for instance, horizontally polarized light has its electric field aligned with the ground, while vertically polarized light has its electric field aligned perpendicular to the ground. In between, we can have diagonal and anti-diagonal polarized light.