Direct measurement of the quantum wavefunction
By Jeff S. Lundeen, B. Sutherland, Aabid Patel, C. Stewart, C. Bamber. Nature, 2011
718 citations recorded by the source corpus.
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.
Subfields: Archeology
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Citations in the corpus
- Do We Really Understand Quantum Mechanics? (2012, methodology): “1) [382–384], which has been used to determine the “wave function” of single photons with the appropriate use of small birefringent phase shifter, a Fourier filter, and polarization measurements [385].”
- Nonperturbative theory of weak pre-and post-selected measurements (2011, methodology): “me, using Eqs. (8.75) and (8.76), or in the strongly-nonlinear regime, using Eqs. (8.73) and (8.74) (see Sec. 6.8). The linear-response version of this method was demonstrated9 experimentally in Ref. [102]. Table 7 lists also several other possible meter configuratio ns. In particular, configuration 3”