Schrodinger’s Cat Lives

If quantum physics always sounded a little squirrelly to you, take heart. Yale researchers have announced that they can do what quantum physics claimed to be impossible: they can determine the state a quantum system will collapse to before it happens. This contradicts Schrodinger’s famous hypothetical cat that is superimposed as 50% alive and 50% dead at the same time. The research appears in Nature.

Schrodinger argued that until you open the box, the cat is half alive and half dead in the same way that a qubit can be in 50% of one state or another. When you observe it, you force the system to one state. Researchers at Yale, however, have found a way to use microwaves to indirectly monitor qubits to determine their state prior to the system making a jump. Unlike a normal observation which occurs too late, the Yale technique allows researchers to change the future state to their choice.

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You’re Listening To Quantum Radio

Researchers at Delft University of Technology have created a detector that enables the detection of a single photon’s worth of radio frequency energy. The chip is only 10 mm square and the team plans to use it to explore the relationship of mass and gravity to quantum theory.

The chip has immediate applications in MRI and radio astronomy. Traditionally, detecting a single photon at radio frequencies is difficult due to the significance of thermal fluctuations. At lower frequencies, cryogenic cooling can reduce the issue, but as frequency increases the fluctuations are harder to tame.

The trick requires a qubit that samples the radio frequency energy. While the radio source is at 173 MHz, the qubit is at 1 GHz, allowing a fine time resolution. Coupling of the two is via an LC circuit that uses a Josephson junction which, of course, requires very cold temperatures. Continue reading “You’re Listening To Quantum Radio”

Quantum Computing For Computer Scientists

Quantum computing is coming, so a lot of people are trying to articulate why we want it and how it works. Most of the explanations are either hardcore physics talking about spin and entanglement, or very breezy and handwaving which can be useful to get a little understanding but isn’t useful for applying the technology. Microsoft Research has a video that attempts to hit that spot in the middle — practical information for people who currently work with traditional computers. You can see the video below.

The video starts with basics you’d get from most videos talking about vector representation and operations. You have to get through about 17 minutes of that sort of thing until you get into qubits. If you glaze over on math, listen to the “index array” explanations [Andrew] gives after the math and you’ll be happier.

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Google Ups The Ante In Quantum Computing

At the¬†American Physical Society conference in early March, Google announced their Bristlecone chip was in testing. This is their latest quantum computer chip which ups the game from 9 qubits in their previous test chip to 72 — quite the leap. This also trounces IBM and Intel who have 50- and 49-qubit devices. You can read more technical details on the Google Research Blog.

It turns out that just the number of qubits isn’t the entire problem, though. Having qubits that last longer is important and low-noise qubits help because the higher the noise figure, the more likely you will need redundant qubits to get a reliable answer. That’s fine, but it does leave fewer qubits for working your problem.

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Quantum Computing Hardware Teardown

Although quantum computing is still in its infancy, enough progress is being made for it to look a little more promising than other “revolutionary” technologies, like fusion power or flying cars. IBM, Intel, and Google all either operate or are producing double-digit qubit computers right now, and there are plans for even larger quantum computers in the future. With this amount of inertia, our quantum computing revolution seems almost certain.

There’s still a lot of work to be done, though, before all of our encryption is rendered moot by these new devices. Since nothing is easy (or intuitive) at the quantum level, progress has been considerably slower than it was during the transistor revolution of the previous century. These computers work because of two phenomena: superposition and entanglement. A quantum bit, or qubit, works because unlike a transistor it can exist in multiple states at once, rather than just “zero” or “one”. These states are difficult to determine because in general a qubit is built using a single atom. Adding to the complexity, quantum computers must utilize quantum entanglement too, whereby a pair of particles are linked. This is the only way for any hardware to “observe” the state of the computer without affecting any qubits themselves. In fact, the observations often don’t yet have the highest accuracy themselves.

There are some other challenges with the hardware as well. All quantum computers that exist today must be cooled to a temperature very close to absolute zero in order to take advantage of superconductivity. Whether this is because of a reduction in thermal noise, as is the case with universal quantum computers based on ion traps or other technology, or because it is possible to take advantage of other interesting characteristics of superconductivity like the D-Wave computers do, all of them must be cooled to a critical temperature. A further challenge is that even at these low temperatures, the qubits still interact with each other and their read/write devices in unpredictable ways that get more unpredictable as the number of qubits scales up.

So, once the physics and the refrigeration are sorted out, let’s take a look at how a few of the quantum computing technologies¬†actually manipulate these quantum curiosities to come up with working, programmable computers. Continue reading “Quantum Computing Hardware Teardown”

Ion Trap Makes Programmable Quantum Computer

The Joint Quantum Institute published a recent paper detailing a quantum computer constructed with five qubits formed from trapped ions. The novel architecture allows the computer to accept programs for multiple algorithms.

Quantum computers make use of qubits and trapped ions–ions confined with an electromagnetic field–are one way to create them. In particular, a linear radio frequency trap and laser cooling traps five ytterbium ions with a separation of about 5 microns. To entangle the qubits, the device uses 50 to 100 laser pulses on individual or pairs of ions. The pulse shape determines the actual function performed, which is how the device is programmable. The operations depend on the sequence of laser pulses that activate it. Continue reading “Ion Trap Makes Programmable Quantum Computer”