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Simulating chemical processes is one of the most promising applications of quantum computers, but problems with noise have prevented nascent quantum systems from outperforming conventional computers on such tasks. Now, researchers at Google have taken a major step towards this goal by using the most powerful quantum computer yet built to successfully implement a protocol for calculating the electronic structure of a molecule. The results may form a blueprint for complex, useful calculations on quantum computers affected by noise.

In October 2019, Google announced to great fanfare that its 53-qubit Sycamore computer had achieved quantum advantage. This means that a quantum computer can solve at least one problem much faster than any conventional supercomputer. However, Google researchers openly acknowledged that the problem Sycamore solved (sampling the outcome of a random quantum circuit) is easy for a quantum computer but difficult for a conventional supercomputer — and had little practical use.

What researchers would really like to do is use quantum computers to solve useful problems more effectively than possible with conventional computers: “Sycamore is extremely programmable and, in principle, you really can run any algorithm on it…In this sense, it’s a universal quantum computer,” explains team member Ryan Babbush of Google Research, “However, there’s a heavy caveat: there’s still noise affecting the device and as a result we’re still limited in the size of circuit we can implement.” Such noise, which results from classical sources such as thermal interference, can destroy the fragile superpositions crucial to quantum computation: “We can implement a completely universal circuit before the noise catches up and eventually destroys the computation,” says Babbush.

New experimental evidence of a collective behavior of electrons to form “quasiparticles” called “anyons” has been reported by a team of scientists at Purdue University.

Anyons have characteristics not seen in other subatomic particles, including exhibiting fractional charge and fractional statistics that maintain a “memory” of their interactions with other quasiparticles by inducing quantum mechanical phase changes.

Postdoctoral research associate James Nakamura, with assistance from research group members Shuang Liang and Geoffrey Gardner, made the discovery while working in the laboratory of professor Michael Manfra is a Distinguished Professor of Physics and Astronomy, Purdue’s Bill and Dee O’Brien Chair Professor of Physics and Astronomy, professor of electrical and computer engineering, and professor of materials engineering. Although this work might eventually turn out to be relevant to the development of a quantum computer, for now, Manfra said, it is to be considered an important step in understanding the physics of quasiparticles.

Xanadu, a photonic quantum computing company, announced today the release of the world’s first publicly available photonic quantum cloud platform, according to a press release. Developers can now access Xanadu’s gate-based photonic quantum processors, in 8, 12, and soon 24-qubit machines.

Photonics based quantum computers have many advantages over older platforms. Xanadu’s quantum processors operate at room temperature. They can easily integrate into existing fiber optic-based telecommunication infrastructure, enabling a future where quantum computers are networked. It also offers great scalability supporting fault tolerance, owing to robust error-resistant physical qubits and flexibility in designing error correction codes. Xanadu’s unique type of qubit is based on squeezed states – a special type of light generated by our own chip-integrated silicon photonic devices.

“We believe that photonics offers the most viable approach towards universal fault-tolerant quantum computing with Xanadu’s ability to network a large number of quantum processors together. We are excited to provide this ecosystem, a world-first for both quantum and classical photonics,” said Christian Weedbrook, Xanadu Founder and CEO. “Our architecture is new, designed to scale-up like the Internet versus traditional mainframe-like approaches to quantum computing.”

A downsized version of the company’s Sycamore chip performed a record-breaking simulation of a chemical reaction.

Spiros Michalakis is the Caltech quantum physicist who served as the science advisor on Bill & Ted: Face The Music and he was kind enough to sit down and chat about quantum physics, the nature of time, and the brilliant minds behind Bill & Ted.

Check out IQIM at http://www.iqim.caltech.edu

Continue reading “The Science Advisor on Bill & Ted: Face The Music on Time Travel, Entanglement, And Keanu Reeves” »

Although we are currently in an era of quantum computers with tens of noisy qubits, it is likely that a decisive, practical quantum advantage can only be achieved with a scalable, fault-tolerant, error-corrected quantum computer. Therefore, development of quantum error correction is one of the central themes of the next five to ten years. Our article “Topological and subsystem codes on low-degree graphs with flag qubits” [1], published in Physical Review X, takes a bottom-up approach to quantum error correcting codes that are adapted to a heavy-hexagon lattice – a topology that all our new premium quantum processors use, including IBM Quantum Falcon (d=3) and Hummingbird (d=5).

Many in the quantum error correction community pursue a top-down computer science approach, i.e., designing the best codes from an abstract perspective to achieve the smallest logical error rate with minimal resource. Along this path, the surface code is the most famous candidate for near-term demonstrations (as well as mid- to long-term applications) on a two-dimensional quantum computer chip. The surface code naturally requires a two-dimensional square lattice of qubits, where each qubit is coupled to four neighbors.

We started with the surface code architecture on our superconducting devices and demonstrated an error detection protocol as a building block of the surface code around 2015 [2]. While the experimental team at IBM made steady progress with cross-resonance (CR) gates, achieving gate fidelities near 99%, an experimental obstacle appeared along the path of scaling up the surface code architecture. The specific way to operate the CR gates requires the control qubit frequency to be detuned from all its neighboring target qubits, such that the CNOT gates between any pair of control and target can be individually addressed.

New research shows how the next generation of ultra-secure communication could be possible with existing infrastructure.

Capable of connecting eight or more users across distances of 17 kilometers, the demonstration is another milestone toward developing a fully quantum Internet.

When probing the subtle effects of quantum mechanics, all the parameters in the system and its measurements need to be finely tuned to observe the result you are hoping for. So what happens when you gear everything towards detecting what you least expect? Researchers at MIT and Purdue University in the U.S. took just this approach and found they could amplify quantum signals by a factor of 30 while conditionally changing the relative phase of a photon from π/80 to π/2. The results could provide the missing link that nudges a number of quantum network technologies closer to practical use.

Quantum technology protocols generally aim to maximize interaction strengths, but preparing these entangled systems can be very difficult. “We asked the question, can we turn weak interactions into very strong interactions somehow?” explains Vladan Vuletic, Wolf Professor of Physics at MIT. “You can, and the price is, they don’t happen often.”

The effects Vuletic and colleagues observe hinge on the factors that feed into the “expectation values” of quantum experiments. Expectation values describe the average outcome of a quantum scenario and equate to the product of each possible value and its probability. Vuletic and his collaborators focused their studies on scenarios where the average is dominated by rare events, like a lottery where everyone wins a small amount on average, although in fact, just a few people win huge amounts. In quantum mechanics, light also sometimes takes the path less traveled, and as the researchers show, this really can make all the difference.