Quantum Leap in Superconducting Circuitry

UC Berkley researchers have developed a new superconducting circuit that acts quantum mechanically, but takes a nice leap in energy levels (link):

These circuits act like artificial atoms in that they can only gain or lose energy in packets, or quanta, by jumping between discrete energy levels. "In our previous work, we focused on systems with just two energy levels, 'qubits,' because they are the quantum analog of 'bits,' which have two states, on and off," said Matthew Neeley, first author and a graduate student at UCSB.

He explained that in this work they operated a quantum circuit as a more complicated artificial atom with up to five energy levels. The generic term for such a system is "qudit," where 'd' refers to the number of energy levels –– in this case, 'd' equals five.

"This is the quantum analog of a switch that has several allowed positions, rather than just two," said Neeley. "Because it has more energy levels, the physics of a qudit is richer than for just a single qubit. This allows us to explore certain aspects of quantum mechanics that go beyond what can be observed with a qubit."

Just as bits are used as the fundamental building blocks of computers, qubits could one day be used as building blocks of a quantum computer, a device that exploits the laws of quantum mechanics to perform certain computations faster than can be done with classical bits alone. "Qudits can be used in quantum computers as well, and there are even cases where qudits could be used to speed up certain operations with a quantum computer," said Neeley. "Most research to date has focused on qubit systems, but we hope our experimental demonstration will motivate more effort on qudits, as an addition to the quantum information processing toolbox."

- Brewskie

Physicists Plan to Teleport Light

Teleportation of objects and living humans someday will be reality (decades down the road, of course); teleportation of light is, for the moment, a first baby step to that vision (link).

Usually when physicists talk about quantum teleportation, they're referring to the transfer of quantum states from one particle to another without a physical link. Now, physicists have investigated a slightly different form of teleportation, in which they teleport a quantum field, or an entire beam of light, from one location to another. This kind of "strong" teleportation is required for some quantum information applications, and could lead to the teleportation of quantum images.

In their study, Changsuk Noh, M.J. Collett, and H.J. Carmichael from the University of Auckland in New Zealand, along with A. Chia from Griffith University in Queensland, Australia, and Hyunchul Nha from Texas A & M University at Qatar in Dohar, Qatar, have proposed a scheme for teleporting a beam of light, including its fluctuations over time. They hope to show that it’s possible that a physical object (e.g. a quantum field) in one location could emerge at another location in the same quantum state, so that any conceivable measurement would yield the same result in both locations. In contrast, previous teleportation schemes do not seriously consider reproducing certain elements, such as temporal fluctuations.

In their proposal, the scientists investigate using a stream of photons that are evenly spaced, or “antibunched.” Detecting the individual photons in a stream that is spaced similar to the photon stream at the input would verify teleportation of the full quantum field. The scientists wanted to find the conditions under which this detection could occur. They discover that squeezing light - a technique used to enhance precision measurements - could allow for teleportation of a quantum photon stream if the squeezing is across a broad bandwidth.

[...]

The scientists note that the squeezing levels are demanding, but further investigations into designing experiments could reveal more optimal methods. One
of the biggest challenges for realizing the proposal, as Carmichael explained, is the requirement for high quality, flexible sources of squeeze light.

“The technology to realize the scheme is, at the level of fundamentals, already in place; but there are serious challenges in making the technology good enough to carry out an experiment,” he said. “The main step required is to improve the source of squeezed light. Improvements in two directions are needed: first, to achieve higher levels of squeezing, and, second, to squeeze at a high level over a broad bandwidth in the range of frequencies of the input light.”

If physicists can overcome these challenges, the ability to transport light beams could lead to many interesting applications. For instance, the researchers suggest that a multi-channel version - in which two or more beams are teleported in parallel - could be used to teleport quantum images.

- Brewskie