In the quantum world the future affects the past - VIDEO PDF Print E-mail
Friday, 13 February 2015 09:19

The experiment showed that the analysis of the past and future of a quantum system, "predicts" her condition more accurately than simply an analysis of the future. Difficult? Let's face it. We are so accustomed to the detective stories that do not even notice how the author plays with time. Usually murder occurs until the middle of the book, but the reader can see only black spot, and, as a rule, he learns what happened, only on the last page.

If you pull out the last page of the book, according to physicist Boat March from Washington University in St. Louis, as the reader will better understand what happened: after reading until a torn page or read the entire book? The answer is all too obvious in the case of a detective, but not so easy in the world of quantum mechanics, where the uncertainty is fundamental, not attracted to the joy of reading.

Even if you know everything that quantum mechanics can describe quantum particle, says Murch, you can not predict with certainty the outcome of a simple experiment to measure its state. All it has to offer, quantum mechanics, it is the statistical probability of possible outcomes.

Conventional wisdom says that this uncertainty is not a defect of the theory, but rather a fact of nature. State of the particle not only unknown, but in truth is not determined prior to the measurement. Act measurement itself causes particles to collapse to a certain condition.

In the journal Physical Review Letters, the release of which will be held on February 13, March Cather describes a method to narrow the chances of successful definition. By combining information on the evolution of a quantum system after a point of reference with information about its evolution up to this time, a physicist at the laboratory was able to narrow down the chances of a correct definition of the two states of the system with a 50/50 to 90/10.

It is as if what we did today, yesterday changed. And it follows from this analogy, the experimental results are terrible value for the time and caUSAtion - at least in the microscopic world of quantum mechanics.
The measurement of the phantom

Until recently, physicists could explore the quantum-mechanical properties of individual particles only in the process of thought experiments, as any attempt to observe them directly led to the fact that the particles hid their mysterious quantum properties.

In 1980-90 years physicists have invented a device that allows them to measure these fragile systems so carefully that they do not suddenly collapse to a state. The device, which used the March, is a simple superconducting loop, which is a quantum space, when cooled to near absolute zero. March's team used two lowest energy levels of the cube, ground and excited states, in his model of a quantum system. Between these two states have an infinite number of quantum states, which represent the superposition, or a combination of the ground and excited states.

The quantum state of the circuit is detected by placing it in a microwave box. Several microwave photons are sent in a box where their quantum fields interact with a superconducting loop. When the photons leave the box, they carry information about the quantum system.

It is important to note that these "weak", vnerezonansnye not bother measuring the qubit, in contrast to the "strong" measurements with photons, which in resonance with the energy difference between two states knocks the chain in one or another state.
quantum Guess

The paper describes a quantum March guessing a qubit:

     "Every time we start from the premises of a qubit in a superposition of two states, - he said. - Then perform a strong dimension, but hide the result, while continuing to observe the system with weak measurements. "

The researchers then try to guess the hidden result, if the version of murder, which remained on the torn page detective.

     "Calculations for the future with the use of the Born, which express the probability of finding the system in a particular state, guarantee you the chances of a correct answer in 50% of cases, - says Murch. - But you can also find him on the contrary, using a specific matrix effect. Just take all the equations and turn. They will work and you can just run back trajectory. "

     "So, if you look on the back and vperediiduschuyu trajectory and weigh them information equally, we get a forecast retroactively or retrodiktsiyu."

Interesting in this retrognoze (instead of the forecast) that it is 90% accurate. When physicists have tested it on an earlier save the measurement system, they guessed right 9 times out of 10.
Down the rabbit hole

Quantum Guessing can be useful in the development of quantum computers and quantum open systems such as control of chemical reactions, making them more reliable. It may also have implications for the deeper problems in physics.

On the one hand, it suggests that in the quantum world, time flows back and forth, whereas in the classical world, it only flows forward.

     "I always thought that the measurement should address the issue of time symmetry in quantum mechanics, - says Murch. - If we measure a particle in a superposition of states, and it collapses into one of two states, well, it seems that this process - the movement of time ahead. "

But the experiment with quantum guessing returned time symmetry. Improved chances of the forecast mean that the quantum state somehow combines information from the future and the past. This means that the time in the quantum world is represented by a two-headed arrow.

     "It is unclear why in the real world, consisting of a set of particles, time moves only forward and entropy always increases - says Murch. - But many are working on this problem, and I think that it will be resolved in a couple of years. "

Nevertheless, there is a world where time is symmetrical, things like cause and effect? To find out, March offers to run an experiment with a qubit, which will create a feedback loop (the chain of cause and effect), and try to run them back and forth. "In one such experiment will take 20-30 minutes a few weeks to analyze and year scratching turnips and trying to understand, we have gone mad or not. In any case, I comforted by the fact that we have a real experiment and present the data. "



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