Researchers have uncovered a new way to look inside Schrödinger's Box.
In the past, researchers' only option for measuring a 27-dimensional quantum state was to employ the quantum tomography method; this techniques is "similar to creating a 3D image from many 2D ones," which is incredibly tedious and time consuming, a University of Rochester news release reported.
A research team came up with an alternative method, dubbed "direct measurements," to accomplish the same feat over the course of one experiment and with zero post-processing. The technique could allow researchers to quickly and efficiently characterize high-dimensional states. This breakthrough could not only help us understand more about quantum mechanics, but could also allow us to develop a "high security quantum communications system."
"Our work shows that direct measurement offers an exciting alternative to quantum tomography," Robert Boyd, Professor of Optics and Physics at the University of Rochester and Canada Excellence Research Chair in Quantum Nonlinear Optics at the University of Ottawa, said in the news release. "As the field of quantum information continues to advance, we expect direct measurement to play an increasingly important role in this."
National Research Council Canada scientists invented the direct measurement technique in 2011; it has been used in the past to determine the "position and momentum of photons." Last year Rochester and Ottawa researchers showed the technique could also be used to measure the "polarization states of light."
In the past researchers thought these types of measurements would be impossible based on the uncertainty principle, which is the idea that "certain properties of a quantum system could be known with precision only if other properties were known poorly," the news release reported. The direct measurement technique involves a "trick" that overrides the principle.
Direct measurement involves a "weak" measurement followed by a stronger one. In quantum mechanics a "collapse of the wavefunction" means the quantum state has been irreversibly disturbed through measurement. In direct measurement the initial "weak" measurement only mildly disturbs the state.
"It is sort of like peeking into the box to see if Schrodinger's cat is alive, without fully opening the box," lead author Doctor Mehul Malik, currently a post-doctoral research fellow at the University of Vienna, said. "The weak measurement is essentially a bad measurement, which leaves you mostly uncertain about whether the cat is alive or dead. It does, however give partial information on the health of the cat, which when repeated many times can lead to near certain information as to whether the cat is alive or dead."
The weak measurement does not "destroy the system" unlike past techniques, allowing for a follow-up measurement of the other variable. The "weak" and "strong" sequence is then repeated on identical systems until the wave function is known with the "required precision."
