However, one notable difference between the Chinese and American experiments is that the Beijing experiment used a blue laser for their teleportation experiments while the BBN team had been employing infrared. Both have advantages and disadvantages in range and power, but the primary difference in their applications seems to be that blue and blue-green lasers penetrate further into water and so have wider applications for sub-surface communications.
Friday, August 27, 2010
As described here, Chinese researchers have demonstrated teleportation over 16 kilometers. Notable part of the article:
Thursday, August 19, 2010
I have not read through it yet, but the topic and abstract sound interesting: Quantum Steganography and Quantum Error-Correction by Shaw out of University of Southern California. (Ph.D. thesis) Here's the abstract:
(Image is from the paper.)
In the current thesis we first talk about the six-qubit quantum error-correcting code and show its connections to entanglement-assisted error-correcting coding theory and then to subsystem codes. This code bridges the gap between the five-qubit (perfect) and Steane codes. We discuss two methods to encode one qubit into six physical qubits. Each of the two examples corrects an arbitrary single-qubit error. The first example is a degenerate six-qubit quantum error-correcting code. We prove that a six-qubit code without entanglement assistance cannot simultaneously possess a Calderbank-Shor-Steane (CSS) stabilizer and correct an arbitrary single-qubit error. A corollary of this result is that the Steane seven-qubit code is the smallest single-error correcting CSS code. Our second example is the construction of a non-degenerate six-qubit CSS entanglement-assisted code. This code uses one bit of entanglement (an ebit) shared between the sender (Alice) and the receiver (Bob) and corrects an arbitrary single-qubit error. In the second half of this thesis we explore the yet uncharted and relatively undiscovered area of quantum steganography. Steganography is the process of hiding secret information by embedding it in an innocent message. We present protocols for hiding quantum information in a codeword of a quantum error-correcting code passing through a channel. Using either a shared classical secret key or shared entanglement Alice disguises her information as errors in the channel. Bob can retrieve the hidden information, but an eavesdropper (Eve) with the power to monitor the channel, but without the secret key, cannot distinguish the message from channel noise. We analyze how difficult it is for Eve to detect the presence of secret messages, and estimate rates of steganographic communication and secret key consumption for certain protocols.
(Image is from the paper.)
From PhysicsWorld.com: Quantum simulators revealed in fresh detail. What I found the most interesting in the article:
"A Mott insulator with exactly one atom per lattice site represents a very promising candidate for a quantum register of up to a few hundred atomic quantum bits," adds Kuhr. "However, we needed to show that we really are able to manipulate each individual atom in the structure. This is crucial for encoding and reading out qubits and we are now at the beginning of setting up the first experiments of this kind."
There is also an article in Nature here.
Wednesday, August 11, 2010
There's a recent story on Wired titled Tech That Never Took, within it is a short section on quantum computing (third one down here) by Tomas Hayden. It falls under the "tech that never took" category because the idea was introduced nearly three decades ago and our physical implementations are currently only a few handful of qubits at best. In the article Aaronson points out that the hard part of making a quantum computer is decoherence. When building a quantum computer you can think of this problem as basically being an unintended interaction with the environment which results in the state of the quantum computer not being maintained.
It is true that we've been working on it for a long time, but I disagree that quantum computing falls under the category of "tech that never took". It is taking us a long time because it is a really hard problem. Take another hard problem, developing the atomic bomb for example. It took a long time to create one, and we only did so when we did because of the huge amount of resources poured into the Manhattan Project. Another example is classical computers: much more than 3 decades elapsed between Charles Babbage's Difference Engine and the first real computers in the mid-twentieth century. My point is that just because it takes a long time to tackle a problem doesn't mean it will "never [take]".
Additionally we continue to make progress towards quantum computers, as I've outlined multiple times. My area is quantum software, not constructing the hardware, but I'd guess we're around a decade out from our first practical quantum computers. I'd also disagree with several of the other subjects listed in the article: nanotechnology, fusion power, personalized medicine, and self driving cars to name the most glaring ones to me. Given time, we've tackled some amazing problems, I don't see why these and quantum computing will be any different. Before 1903 there wasn't even powered flight by man, by 1969 we were landing people on the Moon.
Tuesday, August 10, 2010
Levy out of the University of Pittsburg received 7.5 million (in US dollars) funding from the US Department of Defense to lead a team "...to tackle some of the most significant challenges preventing the development of quantum computers...". Full article here.
There's an article published yesterday on SFGate by Chopra and Hameroff titled Can science explain the soul? As the title implies it is pretty philosophical, but a large part of the discussion involves quantum mechanics and how they could tie in. Various interpretations and speculations on how quantum processes may have a deeper meaning are always interesting- this one is worth the quick read.