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For The Daily Beast:
It’s like no computer you’ve ever seen, nor are you likely to ever own. It promises speed and the ability to tackle problems ordinary computers can’t handle.
The machine is the D-Wave 2X, and the only working model outside the company is in the Quantum Artificial Intelligence Lab. A joint project between Google, NASA, and the Universities Space Research Association, the lab will test-drive the 2X on some sticky problems in high-powered computing.
The 2X is a type of quantum computer, which means it uses devices that exploit quantum physics to replace transistors and other components of ordinary computers. The quantum nature of the inner workings in theory should make the computer solve problems much faster than anything else available, making it useful for a wide range of applications. While there are no fully quantum computers out yet, the 2X is the closest yet—assuming it works as advertised. [Read the rest at The Daily Beast…]
If you shine light on a barrier with two openings, it produces a distinct pattern of light on a distant screen. Measuring that pattern is standard in introductory physics laboratories. (You could even do it at home, but I recommend a very dark room and a bright laser pointer if you hope to see anything at all.) Where things get fun, though, is if you have a light source capable of sending a slow stream of photons — particles of light — through: you still get the interference pattern, but it emerges slowly from individual points of light. In other words, the photons behave as though the entire wave interference pattern is already present, even though they are single particles.
My latest article for Nautilus shows how researchers have taken this classic experiment, but use single photons to manipulate the interference pattern via the phenomenon known as entanglement. The result is a mind-bending experiment known as the “quantum eraser”:
The best way to see the quantum eraser is to couple the double-slit experiment with another fascinating quantum phenomenon: entanglement. In a typical implementation, light from a laser stimulates a certain kind of crystal, which in turn emits two photons with opposite polarization—one could oscillate left-right, while the other oscillates up-down. (You can see how this works by putting one pair of polarized sunglasses in front of another and rotating one pair. At certain angles, the light going through both lenses will fade to almost nothing, a sign that the light is passing through two filters with perpendicular orientations.)
The polarization of each photon is unknown before measurement, but because of how they’re generated, they are entangled, and measuring one can instantly affect each the other. That holds true no matter how far apart the two particles are or when the measurements are taken. [read more….]
(OK, it doesn’t scan. So sue me.) Quantum entanglement is a challenging topic, and one which has tripped up a lot of people (including many physicists!) over the decades. In brief, entanglement involves two (or more) particles constituting a single system: measurement on one particle instantly determines the result of similar measurements on the second, no matter how far they are separated in space. While no information is transferred in this process, it’s still at odds with our everyday experience with how the world should work. I updated my earlier explanation of entanglement, which hopefully can help clear up some of the confusion.
Recent work either assumes entanglement is real and probes some of the more interesting implications, or tests some mathematical relations known as Bell’s inequalities. The latter are aimed at quantifying the difference between the predictions of quantum physics and certain alternative models. In that spirit, a group of researchers proposed using light from quasars to randomize the measurement apparatus in entanglement experiments, to eliminate the tiny possibility of a weird loophole in quantum theory.
If a detector has some correlation with the hidden variables of the particles being measured, then the two detectors don’t act independently. That’s true even if only a very tiny amount of information is exchanged less than a millisecond before measurements take place. The interaction would create the illusion that the particles are entangled in a quantum sense, when in fact they are influencing the detectors, which in turn dictate what measurements are being taken. This is known as the “detector settings independence” loophole—or somewhat facetiously as the “free will” loophole, since it implies the human experimenter has little or no choice over the detector settings. [Read more…]
Final note: this is probably the first paper I’ve covered that involves both my undergraduate research focus (quantum measurement) and my PhD work (cosmology), albeit in a much different way than both.
I spent much of the week sick, but that doesn’t stop me. I care about you, people.
- All black holes, great and small (Galileo’s Pendulum): As my regular readers have probably figured out, I love black holes. I could probably find an excuse to write about them most days. So, why not take an online class from me and learn about black holes? The class begins this Tuesday (October 1), and runs for four one-hour sessions. Sign up today!
- A Holographic Big Bang: Did the universe start with a five-dimensional black hole? (Slate): Much as I love black holes, however, I cast a skeptical eye on a new paper proposing that the Big Bang had an event horizon. This Slate piece examines what we mean by the “Big Bang model” (which isn’t quite how it’s often described), and the reasons why this five-dimensional theory probably won’t solve the mystery of our Universe’s origins.
- Scientific grumpfiness and open-mindedness (Galileo’s Pendulum): All three pieces I’ve written for Slate thus far, in addition to a number of other articles published elsewhere, are critical responses to scientific reporting. Generally, I find myself on the opposite side to those who promote radical new theories, which makes me worry sometimes that I’m just a naysayer with no positive commentary to make. Here’s my examination of that worry. (Yes, it’s a bit meta, I suppose.)
- Pulsar’s magnetic field strong enough to clean up after nuclear explosion (Ars Technica): While pulsars are all fast-spinning objects, some are extremely so, rotating hundreds or thousands of times each second. A new observation caught one of these pulsars in the act of feeding off material from a companion star, lending strong support to the theory of how they spin so fast. Bonus: runaway nuclear explosions! on the surface of a dead star! Who needs science fiction?
- Snobbish photons forced to pair up and get heavy (Ars Technica): Photons don’t usually interact in the usual sense that matter particles do. Researchers produced a weird medium by pumping a diffuse gas of rubidium atoms with laser light until they puffed up. The result: the interactions between the atoms made an environment where photons have an effective mass (!) and attract each other, forming pairs. Beyond being really cool, this could have all sorts of applications in quantum logic and even “photon materials”.
And just because I can, here’s Cookie Monster playing with his Newton’s cradle again.
Cookie Monster is me brother from another mother.
Often in physics, we can separate the object from the environment and the experimental apparatus from what’s being measured, but that separation is approximate. In quantum systems, those distinctions break down, to the point where the environment “measures” the system, in ways we don’t fully understand even after nearly a century of study. (A lot of nonsense has been written about the subject, too, which is a rant for another day.) A new experiment may help mitigate some of the problems of system-environment interaction, through understanding how photons and atoms couple—and when they do not.
One remaining frontier is comprehension of how systems gradually lose coherence via interactions with their environment, which prevents their usefulness in quantum computing. A new set of experiments by Yinnon Glickman, Shlomi Kotler, Nitzan Akerman, and Roee Ozeri revealed part of the mechanism by which environment disrupts quantum systems: photons. They found that photons that interacted with a quantum system can end up correlated with the system’s state, the hallmark of entanglement. By careful preparation of the atom’s state, it may be possible to reduce the loss of quantum information to the environment, and thus extend the life of these systems. [Read more…]
Quantum entanglement is a weird concept in a theory full of weird concepts. A typical experiment goes as follows: you prepare a pair of photons such that their polarizations are complementary. A subsequent measurement on one photon will reveal the outcome of a related measurement on the other photon—no matter how widely they are separated. A “quantum eraser” takes that idea one step further: one of the photons is sent into an interference device, and measurement on the second determines whether or not interference actually takes place. Researchers constructed a quantum eraser experiment on two of the Canary Islands to show that the two measuring apparatuses can’t communicate with each other.
The quantum eraser experiment involves producing two sets of photons with correlated polarizations. One set, known as the system photons, are sent into a polarizing beam-splitter (PBS); as the name suggests, this directs light along different paths based on its polarization. The two possible paths for the system photon were then recombined, so they could either interfere (if the photon is behaving like a wave) or show up in one of two detectors (behaving like a particle). [Read more…]
Erwin Schrödinger is best known to non-scientists for his thought experiment involving a cat (or maybe his unconventional living arrangement), but he also wrote What is Life?, a book that attempted to bring the fields of physics and biology closer to each other. Today, experiment is beginning to reach the point where we can see if the specifically quantum aspects of physics play a direct role in biology. Even though in a fundamental sense, everything is quantum mechanical, the quantum state—the entity that encodes the probability of the outcomes of various interactions—doesn’t usually need to be considered for biology. However, it’s still possible life has learned to harness quantum effects, ranging from tunneling to entanglement, to gain an evolutionary advantage.
An intriguing aspect of all of these possibilities is that perhaps evolution has figured out a better way of performing tricky quantum manipulations than we have. In a sense, that’s not surprising: life has had a long time to evolve photosynthesis, photoreception, and navigation, while our understanding of quantum mechanics just began in the 1920s and ’30s. [Read more…]