Quantum physics is full of fascinating phenomena. Take, for instance, the cat from the famous thought experiment by the physicist Erwin Schrodinger. The cat can be dead and alive at once, since its life depends on the quantum mechanically determined state of a radioactively decaying atom which, in turn, releases toxic gas into the cat's cage. As long as one hasn't measured the state of the atom, one knows nothing about the poor cat's health either - atom and kitty are intimately "entangled" with each other.
Equally striking, if less well known, are the so-called squeezed quantum states: Normally, Heisenberg's uncertainty principle means that one cannot measure the values of certain pairs of physical quantities, such as the position and velocity of a quantum particle, with arbitrary precision. Nevertheless, nature allows a barter trade:
If the particle has been appropriately prepared, then one of the quantities can be measured a little more exactly if one is willing to accept a less precise knowledge of the other quantity. In this case the preparation of the particle is known as "squeezing" because the uncertainty in one variable is reduced (squeezed).
Schrödinger's cat and squeezed quantum states are both important physical phenomena that lie at the heart of promising technologies of the future. Researchers at the ETH were now able successfully to combine both in a single experiment.
Squeezing and shifting
In their laboratory, Jonathan Home, professor of experimental quantum optics and photonics, and his colleagues catch a single electrically charged calcium ion in a tiny cage made of electric fields. Using laser beams they cool the ion down until it hardly moves inside the cage. Now the researchers reach into their bag of tricks: they "squeeze" the state of motion of the ion by shining laser light on it and by skilfully using the spontaneous decay of its energy states.
Eventually the ion's wave function (which corresponds to the probability of finding it at a certain point in space) is literally squashed: now the physicists have a better idea of where the ion is located in space, but the uncertainty in its velocity has increased proportionately. "This state squeezing is an important tool for us", Jonathan Home explains. "Together with a second tool - the so-called state-dependent forces - we are now able to produce a "squeezed Schrödinger cat" ".
To that end the ion is once more exposed to laser beams that move it to the left or to the right. The direction of the forces induced by the laser depends on the internal energy state of the ion. This energy state can be represented by an arrow pointing up or down, also called a spin. If the ion is in an energy superposition state composed of "spin up" and "spin down", the force acts both to the left and to the right. In this way, a peculiar situation is created that is similar to Schrödinger's cat: the ion now finds itself in a hybrid state of being on the right (cat is alive) and on the left (cat is dead) at the same time. Only when one measures the spin does the ion decide whether to be on the right or on the left.
Stable cats for quantum computers
The Schrödinger cat prepared by professor Home and his collaborators is special in that the initial squeezing makes the ion states "left" and "right" particularly easy to distinguish. At the same time, it is also pretty large as the two ion states are far apart. "Even without the squeezing our "cat" is the largest one produced to date", Home points out.
"With the squeezing, the states "left" and "right" are even more distinguishable - they are as much as sixty times narrower than the separation between them". All this isn't just about scientific records, however, but also about practical applications. Squeezed Schrödinger cats are particularly stable against certain types of disturbances that would normally cause the cats to lose their quantum properties and become ordinary felines. That stability could, for instance, be exploited in order to realize quantum computers, which use quantum superposition states to do their calculations. Furthermore, ultra-precise measurements could be made less sensitive to unwanted external influences.
Lo HY, Kienzler D, de Clercq L, Marinelli M, Negnevitsky V, Keitch, BC, Home JP: Spin-motion entanglement and state diagnosis with squeezed oscillator wavepackets. Nature, 21 May 2015, doi: 10.1038/nature14458 [http://dx.
Dr. Jonathan Home | EurekAlert!
Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore
Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
05.12.2016 | Power and Electrical Engineering
05.12.2016 | Materials Sciences
05.12.2016 | Power and Electrical Engineering