Last updated December 2011 - Any views or opinions expressed on this webpage are my personal views and do not represent those of NRC
Q+ presentation on "Direct Observation of the Wavefunction" is here
I am currently a Research Officer of Quantum Metrology in the Institute for National Measurement Standards (INMS) at the National Research Council (NRC) in Ottawa, which is the capital of Canada. The photo above is of Parliament Hill, the home of Canada's government. I work with Charles Bamber at INMS, Robin Williams at the Institute for Microstructural Sciences (IMS) and Ben Sussman at the Steacie Institute for Molecular Science (SIMS) as well as an accomplished team of scientists, students, and technicians on radiometric standards, quantum dot single-photon sources, quantum information, and quantum metrology.
News
Direct Measurement of the Quantum Wavefunction is published in Nature!Chosen as 2nd most important Physics Breakthrough of 2011 by Physics World!
- Here is our paper freely available on the arXiv: Free Version
- Direct link to the paper on the Nature site is HERE
- Technical summary: Onur Hosten has written a nice News and Views in Nature
- A review article in Science on recent weak measurement experiments including ours: Furtive Approach Rolls Back the Limits of Quantum Uncertainty by Adrien Cho
- National Research Council English Press Release
- National Research Council French Press Release
- An excellent French language summary and discussion: Mettre le doigt sur l’insaisissable by Jean-François Cliche
- And a great explanation at ScienceNews by Devin Powell: Wave function directly measured Physicists reach out and touch an equation.
- Tushna Commissariat at physicsworld.com has written a nice summary with more information about how the experiment worked: Catching sight of the elusive wavefunction
- Summaries by Charles Bamber and myself: Semi-technical explanation and Non-technical explanation
Jeff S. Lundeen, Brandon Sutherland, Aabid Patel, Corey Stewart, & Charles Bamber
Direct measurement of the Quantum Wavefunction
Nature, pp 188-190, 474 (2011).
Abstract:
The wavefunction is the complex distribution used to completely describe a quantum system, and is central to quantum theory. But despite its fundamental role, it is typically introduced as an abstract element of the theory with no explicit definition. Rather, physicists come to a working understanding of the wavefunction through its use to calculate measurement outcome probabilities by way of the Born rule. At present, the wavefunction is determined through tomographic methods, which estimate the wavefunction most consistent with a diverse collection of measurements. The indirectness of these methods compounds the problem of defining the wavefunction. Here we show that the wavefunction can be measured directly by the sequential measurement of two complementary variables of the system. The crux of our method is that the first measurement is performed in a gentle way through weak measurement, so as not to invalidate the second. The result is that the real and imaginary components of the wavefunction appear directly on our measurement apparatus. We give an experimental example by directly measuring the transverse spatial wavefunction of a single photon, a task not previously realized by any method. We show that the concept is universal, being applicable to other degrees of freedom of the photon, such as polarization or frequency, and to other quantum systems—for example, electron spins, SQUIDs (superconducting quantum interference devices) and trapped ions. Consequently, this method gives the wavefunction a straightforward and general definition in terms of a specific set of experimental operations. We expect it to expand the range of quantum systems that can be characterized and to initiate new avenues in fundamental quantum theory.
Quantum Information and Metrology with Photons
In the Institute for Microstructural Sciences, I am helping to develop quantum dot sources of single-photons and entangled photon pairs. Our InAs dots are particularly nice because they are grown (at NRC) on the top of InP pyramids.
Arrays of these pyramids are fabricated giving us
quantum dots grown in array of positions, known to within 10 nm or so.
This means the dots can be placed precisely in the antinode of an
optical cavity. The optical cavities vary in type but we use 2-d photon
crystal cavities. These are an array of holes, drilled into InP. This
structure is made to inhibit optical emission of the quantum dot. A
defect in the structure then acts as a cavity, capturing the emitted
single-photons and, with careful design, channeling them towards an
optical fiber. From that point we can use these photons as carries of
information and, in the future, use them to build quantum computers or
in quantum cryptography. The picture shows a) an array of dots on a
ridge, b) a single dot on top of pyramid, c) electrical gates
isolating a single dot on the ridge, d) a pyramid with gates on it. The
gates allow us to mamipulate the levels and, thus, the emission of the
dot.
Quantum metrology is the study of measurement using the theory of quantum physics. This can mean a few things: 1. Determing the ultimate sensitivity limit of a measurement. 2. Using inherently quantum systems to enable enhansed sensitivity measurements. 3. Performing new types of measurment that would be impossible without quantum physics. At the Institute for National Measurement Standards I am involved in an ambitious project, led by Charles Bamber, to develop quantum metrology with light into practical services that we can offer to researchers and industry. We also will be working to further develop the science of quantum metrology. We are currently building sources of photon pairs (these emit the concentric pattern of colours shown above, from Marlan Scully's book Quantum Optics), a characterization system for quantum dots, ultrafast pump lasers and other tools needed to do quantum metrology.