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“Until now researchers have encoded and stabilized. We now show that we can compute as well.”

Researchers at QuTech—a collaboration between the TU Delft and TNO—have reached a milestone in quantum error correction. They have integrated high-fidelity operations on encoded quantum data with a scalable scheme for repeated data stabilization. The researchers report their findings in the December issue of Nature Physics.

Physical quantum bits, or qubits, are vulnerable to errors. These errors arise from various sources, including quantum decoherence, crosstalk, and imperfect calibration. Fortunately, the theory of quantum error correction stipulates the possibility to compute while synchronously protecting quantum data from such errors.

The world is an intricate web of interrelations, such that objects no longer have their own individual existence independent from other objects — like an endless game of quantum mirrors.

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The many-worlds interpretation of quantum mechanics predicts the formation of distinct parallel worlds as a result of a quantum mechanical measurement. Communication among these parallel worlds would experimentally rule out alternatives to this interpretation. A procedure for “interworld’’ exchange of information and energy, using only state of the art quantum optical equipment, is described. A single ion is isolated from its environment in an ion trap. Then a quantum mechanical measurement with two discrete outcomes is performed on another system, resulting in the formation of two parallel worlds. Depending on the outcome of this measurement the ion is excited from only one of the parallel worlds before the ion decoheres through its interaction with the environment. A detection of this excitation in the other parallel world is direct evidence for the many-worlds interpretation.

By Alex Hill, Senior Quantum Systems Engineer

Qubits are the basic building block of a quantum processor, and are so named because they represent a continuum of complex superpositions of two basic quantum states. The power of qubits comes in part from their ability to encode significantly more information than a classical bit — an infinite set of states between 0 and 1. In mathematical terms, quantum gates that manipulate the state of individual qubits are unitary operators drawn from SU.

Rigetti’s superconducting quantum processors are based on the transmon design [1]. Each physical qubit is an anharmonic oscillator, meaning that the energy gaps between subsequent qubit energy states decrease as the qubit climbs higher up the state ladder. We typically only address the first two states, 0 and 1 (in the literature, sometimes referred to as g(round) and e(xcited)); however, the design of our qubits supports even higher states. The simple structure of the transmon energy levels gives superconducting qubits the unique ability to address many of these states in a single circuit.

We suggest an interpretation of quantum mechanics, inspired by the ideas of Aharonov et al. of a time-symmetric description of quantum theory. We show that a special final boundary condition for the Universe, may be consistently defined as to determine single classical-like measurement outcomes, thus solving the “measurement problem”. No other deviation is made from standard quantum mechanics, and the resulting theory is deterministic (in a two-time sense) and local. Quantum mechanical probabilities are recovered in general, but are eliminated from the description of any single measurement. We call this the Two-time interpretation of quantum mechanics. We analyze ideal measurements, showing how the quantum superposition is, in effect, dynamically reduced to a single classical state via a “two-time decoherence” process.

In this paper we present the two-state vector formalism of quantum mechanics. It is a time-symmetrized approach to standard quantum theory particularly helpful for the analysis of experiments performed on pre-and post-selected ensembles. Several peculiar effects which naturally arise in this approach are considered. In particular, the concept of “weak measurements’’ (standard measurements with weakening of the interaction) is discussed in depth revealing a very unusual but consistent picture. Also, a design of a gedanken experiment which implements a kind of quantum “time machine’’ is described. The issue of time-symmetry in the context of the two-state vector formalism is clarified.

During NeurIPS 2021, seven quantum computer scientists from Amazon came together to discuss the current state of quantum computing, some of the biggest challenges facing the field, and what the future might hold.

Panelists included:
• Simone Severini, director of quantum computing.
• Antia Lamas-Linares, principal research scientist.
• Earl Campbell, senior research scientist.
• John Preskill, Amazon Scholar.
• Katharine Hyatt, applied scientist.
• James Whitfield, Amazon Visiting Academic.
• Helmut Katzgraber, senior practice manager.

Continue reading “The challenge and promise of quantum computing | Amazon Science” »

The ultra-slippery nature of a two-dimensional material called magnetene could be down to quantum effects rather than the mechanics of physical layers sliding across each other, say researchers at the University of Toronto in Canada and Rice University in the US. The result sheds light on the physics of friction at the microscopic scale and could aid the development of reduced-friction lubricants for tiny, implantable devices.

Two-dimensional materials are usually obtained by shaving atomically thin slices from a sample of the bulk material. In graphene, a 2D form of carbon that was the first material to be isolated using this method, the friction between adjacent layers is very low because they are bound together by weak van der Waals forces, and therefore slide past each other like playing cards fanning out in a deck. For magnetene, the bulk material is magnetite, a form of iron oxide with the chemical formula Fe₃O₄that exists as a 3D lattice in the natural ore. The bonds between layers are much stronger in magnetene than in graphene, however, so its similarly low-friction nature was a bit of a mystery.

A tardigrade cooled to near absolute zero and placed in a state of quantum entanglement survived its ordeal.