Synopsis: The Certainty of Uncertainty

State of the art quantum measurements show that the original formulation of Heisenberg’s uncertainty principle can be violated.
Synopsis figure
L. A. Rozema et al. Phys. Rev. Lett. (2012)

When first taking quantum mechanics courses, students learn about Heisenberg’s uncertainty principle, which is often presented as a statement about the intrinsic uncertainty that a quantum system must possess. Yet Heisenberg originally formulated his principle in terms of the “observer effect”: a relationship between the precision of a measurement and the disturbance it creates, as when a photon measures an electron’s position. Although the former version is rigorously proven, the latter is less general and—as recently shown—mathematically incorrect. In a paper in Physical Review Letters, Lee Rozema and colleagues at the University of Toronto, Canada, experimentally demonstrate that a measurement can in fact violate Heisenberg’s original precision-disturbance relationship.

If the observer affects the observed, how can one even make such a measurement of the disturbance of a measurement? Rozema et al. use a procedure called “weak” quantum measurement: if one can probe a quantum system by means of a vanishingly small interaction, information about the initial state can be squeezed out with little or no disturbance. The authors use this approach to characterize the precision and disturbance of a measurement of the polarizations of entangled photons. By comparing the initial and final states, they find that the disturbance induced by the measurement is less than Heisenberg’s precision-disturbance relation would require.

While the measurements by Rozema et al. leave untouched Heisenberg‘s principle regarding inherent quantum uncertainty, they expose the pitfalls of its application to measurements’ precision. These results not only provide a demonstration of the degree of precision achievable in weak-measurement techniques, but they also help explore the very foundations of quantum mechanics. – David Voss


More Features »


More Announcements »

Subject Areas

Quantum InformationQuantum Physics

Previous Synopsis

Quantum Physics

An Anyon Detector

Read More »

Next Synopsis

Nonlinear Dynamics

Alphabet Waves

Read More »

Related Articles

Viewpoint: Linking Two Quantum Dots with Single Photons

Viewpoint: Linking Two Quantum Dots with Single Photons

Researchers have transferred quantum information from one quantum dot to another dot 5 m away using photonic qubits as the relay. Read More »

Synopsis: Speeding Up Battery Charging with Quantum Physics
Quantum Physics

Synopsis: Speeding Up Battery Charging with Quantum Physics

Calculations show that charging a set of batteries can go faster if the batteries are coupled together quantum mechanically. Read More »

Viewpoint: Photonic Hat Trick

Viewpoint: Photonic Hat Trick

Two independent groups have provided the first experimental demonstration of genuine three-photon interference. Read More »

More Articles