Quantum Mechanics in Photosynthesis

Thanks to Michael for sending me this link:

Physicists have evidence about quantum processes that allow photosynthesis to take place in plants. The article can be found at:

http://arstechnica.com/science/news/2011/12/more-evidence-found-for-quantum-physics-in-photosynthesis.ars?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+arstechnica%2Findex+%28Ars+Technica+-+Featured+Content%29

One of the More Interesting Quantum Experiments!

Thanks to Jeff for forwarding this article.

We all now know that quantum mechanics is bizarre. One of the more incredible predictions and requirements of this theory is that the once thought concept of empty space, or the vacuum of space, is in fact teaming with activity. The concept of virtual particles lies at the heart of quantum field theories, with unobservable particles zooming in and out of existence, allowed by the uncertainty principle (you know things are weird when uncertainty is a rule of Nature!). Uncertainty allows for brief violations of the conservation of energy and momentum.

A team of scientists have published a paper stating they have measured the dynamical Casimir effect. This states that high-speed motion in a vacuum should be able to transfer some of its energy to virtual photons, and force those unobservables into observables! Here is the abstract from the paper, which has yet to be formally peer-reviewed and published in Nature.

"One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. While initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences, for instance producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed if it might instead be possible to more directly observe the virtual particles that compose the quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. This effect was later named the dynamical Casimir effect (DCE). Using a superconducting circuit, we have observed the DCE for the first time. The circuit consists of a coplanar transmission line with an electrical length that can be changed at a few percent of the speed of light. The length is changed by modulating the inductance of a superconducting quantum interference device (SQUID) at high frequencies (~11 GHz). In addition to observing the creation of real photons, we observe two-mode squeezing of the emitted radiation, which is a signature of the quantum character of the generation process. "

Find the whole article here.

Searching for Gravity Waves Using 'Squeezed Light'

There is a neat article (click here) that describes a new technique that is to be used to search for gravitational radiation, the strange effect predicted by Einstein some 90 years ago in his general theory of relativity. The essence of this technique of 'squeezed light' is that a special crystal splits a photon into two, meaning they are then entangled. It is the entanglement that can amplify the effect and sensitivity of the detector, and distinguish an unbelievably weak effect from gravitational waves from the effects of the vacuum (such as virtual photons being produced out of the vacuum of space - something called quantum fluctuations).

This is obviously weird. The concepts come out of the mathematics of quantum mechanics, certainly no easy task to solve. While that may not be so comprehensible to you right now, just know that these strange predictions have been confirmed in countless experiments over the past century. As technology continues to advance, fields such as quantum computing and quantum optics continue to progress, and in this case may help in the construction of the most sensitive measuring device ever built to try and test Einstein's predictions about gravitational radiation. It will be fun to see this develop and, perhaps, produce one more staggering confirmation about Einstein's theories from nearly a century ago. Stay tuned...

Trying to Make Some Sense About Quantum Mechanics

Gaining any level of understanding of quantum mechanics is one of the great intellectual challenges in science. In a quantum world of indeterminism and probability, uncertainty and fuzziness, phenomena completely unseen in our everyday lives are the norm for atoms and particles.

At the center of the strangeness is particle-wave duality, the notion that particles can at times act like ‘solid’ balls, but in different circumstances can behave like a wave. Likewise, something we normally think of as a wave, such as light, can certainly act like a wave under certain conditions, but in quantum mechanics light can also behave like particles we refer to as photons. In fact, a favorite question I pose to students is, ‘When light is traveling from a light bulb to your eye, is it a particle or wave?’ Ultimately, someone will offer the answer, ‘It is both!’ That is an acceptable answer; but what does this mean? How can an ‘object’ be two things simultaneously, which is what the answer ‘both’ implies.

No one is comfortable with this answer, and yet it fits in with the foundational principles of quantum mechanics. The reason is, in the mathematics of quantum mechanics, objects are described with a wave function. This is a mathematical function that encompasses possible states the object can take. So a photon that is moving through space can be thought of as a combination of two states, something like Photon = [particle state] + [wave state]. More specifically, this function can be used to determine the probability of finding the photon in a particle or wave state.

But I think most of us still come back to the same questions: How do we interpret this mathematical nonsense? What does this mean for the object? This is where an analogy comes in handy, that will perhaps put this probabilistic concept into a more understandable context.

If I am talking about this in a class, I ask students to look around at each other and identify the personality snapshot of each of their classmates. This means to identify who is happy, sad, confused, angry, sarcastic, sleepy, bored, or anything else. So while there are numerous possible ‘personality states’ any person can have, while observing a person we can select one personality state at that time because we are interacting with them. However, what do we do when the bell rings and everyone goes on their way? If I ask someone to identify which personality state a specific person is in when they are no longer available for observation or interaction, what is the answer? The best we can do is to effectively guess…but to do this mathematically, we would acknowledge that at any given moment when a person is not being observed in any way, we cannot be certain about the personality state and can only try to identify the probability of that person being in each state. Perhaps there is a 20% chance she is happy, and 25% chance of being sad, and so on for each possible personality state.

This is the way we think about particles and waves when those entities are not being observed. When we do observe the entity, the act of observing selects out the personality from the mix of possible personalities. Another way of saying it is the experiment we do selects out a single observable state that we then identify. For a person, maybe it is the ‘happy’ state that becomes crystallized out of the ‘personality state’ function that includes all the possible personality states. For an electron, if we put it through a diffraction grating the wave personality is selected, whereas if we shoot it at an atom and it is deflected, the particle personality was selected instead.

Thinking this way is not necessarily normal, obvious or instinctive, but it is something we can try to understand the way the quantum world works. Of course, in real quantum mechanical problems, the mathematics becomes very hard very fast, but trying to find more concrete ways of thinking about the consequences of probabilistic concepts can only help the student to whom this is all new.

Quantum Teleportation

Thanks to Nathan for finding this link:

Scientists at the University of Tokyo have done the equivalent of quantum teleportation with quantum bits (qubits) of information. Check out the article, which has some internal links as well. This could be a major discovery in the development of quantum computing, so it will be interesting to see where it leads in the next few years. These are all related to the completely wacky world of quantum mechanics, some of which we have discussed in class.