Quantum Mechanics
A quantum memory may be all scientists need to beat the limit of Heisenberg's uncertainty
principle, according to a paper published in Nature Physics. According to a group of researchers,
maximally entangling a particle with a quantum memory and measuring one of the particle's
variables, like its position, should snap the quantum memory in a corresponding state, which
could then be measured. This would allow them to do something long thought verboten by the
laws of physics: figure out the state of certain pairs of variables at the exact same time with an
unprecedented amount of certainty.
Our ability to observe particles at the quantum level is currently limited by Heisenberg's
uncertainty principle. Heisenberg noticed that when someone measured one variable of a
particle, such as its position, there were some other variables, like momentum, that could not be
simultaneously measured with as much precision—there was a small amount of uncertainty
applied to one or both of the measurements.
The physical reasoning behind this is hard to follow. But Paul Dirac, another physicist, made up
a scenario to illustrate why some variables have this contentious relationship.
Dirac pointed out that one of the only ways to measure a particle's position is by bouncing a
photon off of it, and seeing where and how that photon lands on a detector. How the photon
lands completely describes the particle's position, but by hitting it, the measurement changes the
particle's momentum.
Likewise, a measure of momentum would change the particle's position. Because of this quirk,
scientists thought it was impossible to know certain pairs of variables that affect one another at
the same exact time with a very high degree of precision.
Then along came entanglement. When two particles are entangled, reading even one variable of
one of the particles collapses the wavefunction of both particles, giving finite values to all related
variables.
The cadre of scientists behind the current paper realized that, by using the process of
entanglement, it would be possible to essentially use two particles to figure out the complete
state of one. They might even be able to measure incompatible variables like position and
momentum. The measurements might not be perfectly precise, but the process could allow them
to beat the limit of the uncertainty principle.
The system the researchers worked out involves maximally entangling a particle with a quantum
memory, meaning all states and all degrees of freedom in the particle would be tied to all of the
quantum memory's states. Once they were entangled and separated, an observer would make a
measurement of one of the particle's properties, and then tell the keeper of the quantum memory
which variable they measured.
In theory, there should be a measurement of the quantum memory that would yield the same
result as the measurement done on the particle. The uncertainty relation between the
measurement and any other incompatible variables wouldn't be present in the quantum memory,
however, allowing observers to see exact measurements for two incompatible variables at the
exact same instant in time.
Of course, the operative phrase here is "in theory." The research paper, thought a bit esoteric and
lacking in detail, supports its argument with math involving Hilbert systems and entropy. But no
experiment has yet taken place because our equipment isn't advanced enough yet.