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Category: quantum physics

The race toward the first practical quantum computer is in full stride. Companies, countries, collaborators, and competitors worldwide are vying for quantum supremacy. Google says it’s already there. But what does that mean? How will the world know when it’s been achieved?

Using , at PNNL have set a mark that a quantum system would need to surpass to establish quantum supremacy in the realm of chemistry.

That’s because the fastest classical computers available today are getting better and better at simulating what a quantum computer will eventually be expected to do. To prove itself in the real world, a quantum computer will need to be able to outdo what a fast supercomputer can do. And that’s where the PNNL-led team have set a benchmark for quantum computers to beat.

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Can we realize non-trivial condensed-matter phases – such as topological insulating phases – in the time dimension? Topological insulators are condensed-matter systems that are insulators in their interior but, by virtue of the topological properties of the electronic structure, have conducting surface (edge) states. They are characterized by global topological invariants. An example of a topological invariant is the number of holes a surface has: a sphere has no holes while a torus has one. It is hard to change such a topological invariant because it is not possible to gradually introduce a hole in a sphere in order to change it to a torus – either there is a hole or there is no hole, but there is nothing like a fraction of a hole. Even the vacuum (empty space) has trivial topological invariants. In order to reconcile a change of this invariant at the interface between the vacuum and a topological insulator, there are surface (edge) states that close the gap between the energy bands of the insulator, thereby producing conducting behaviour.

Can a quantum swing behave like an electron in a topological insulator? Yes, for example if we ask the child to push with a combination of a resonant frequency ω and a sub-harmonic frequency ω /2 (Optica 5 1390, New J. Phys. 21 052003). Then the motion of the swing effectively creates a chain of lattice sites along the resonant orbit with staggered hopping amplitudes, and thus reproduces an example of a topological system, called the Su–Schrieffer–Heeger lattice. In order to observe the edge states, we need to create an “edge” in the motion of the swing and then check if there are quantum states that are localized close to it. How can we create an edge in time? We ask the child to jump on the swing from time to time, which introduces a barrier in the chain of lattice sites along the resonant orbit and consequently breaks the time-translational symmetry along the orbit, similar to how a surface breaks spatial-translational symmetry in an ordinary topological insulator.

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Simulating computationally complex many-body problems on a quantum simulator has great potential to deliver insights into physical, chemical and biological systems. Physicists had previously implemented Hamiltonian dynamics but the problem of initiating quantum simulators to a suitable quantum state remains unsolved. In a new report on Science Advances, Meghana Raghunandan and a research team at the institute for theoretical physics, QUEST institute and the Institute for quantum optics in Germany demonstrated a new approach. While the initialization protocol developed in the work was largely independent of the physical realization of the simulation device, the team provided an example of implementing a trapped ion quantum simulator.

Quantum simulation is an emergent technology aimed at solving important open problems relative to high-temperature superconductivity, interacting quantum field theories or many-body localization. A series of experiments have already demonstrated the successful implementation of Hamiltonian dynamics within a quantum simulator—however, the approach can become challenging across quantum phase transitions. In the new strategy, Raghunandan et al. overcame this problem by building on recent advances in the use of dissipative quantum systems to engineer interesting many-body states.

Almost all many-body Hamiltonians of interest remain outside a previously investigated class and therefore require generalization of the dissipative state preparation procedure. The research team therefore presented a previously unexplored paradigm for the dissipative initialization of a quantum simulator by coupling the many-body system performing the quantum simulation to a dissipatively driven auxiliary particle. They chose the energy splitting within the auxiliary particle to become resonant with the many-body excitation gap of the system of interest; described as the difference of the ground-state energy and the energy of the first excited state. During such conditions of resonance, the energy of the quantum simulator could be transferred efficiently to the auxiliary particle for the former to be cooled sympathetically, i.e., particles of one type, cooled particles of another type.

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Our current, well-established understanding of phases of matter primarily relates to systems that are at or near thermal equilibrium. However, there is a rich world of systems that are not in a state of equilibrium, which could host new and fascinating phases of matter.

Recently, studies focusing on systems outside of have led to the discovery of new phases in periodically driven quantum systems, the most well-known of which is the discrete time crystal (DTC) phase. This unique phase is characterized by collective subharmonic oscillations arising from the interplay between many-body interactions and non-equilibrium driving, which leads to a loss of ergodicity.

Interestingly, subharmonic oscillations are also known to be a characteristic of dynamical systems, such as predator-prey models and parametric resonances. Some researchers have thus been exploring the possibility that these may exhibit similar features to those observed in the DTC phase.

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A team of scientists in Australia claim to have stumbled on a breakthrough discovery that will have “major implications” for the future of quantum computing.

Describing the find as a “happy accident,” engineers at the University of New South Wales Sydney found a way to control the nucleus of an atom using electric fields rather than magnetic fields—which they have claimed could now open up a “treasure trove of discoveries and applications.”

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Morello and colleagues studied an antimony nucleus embedded in silicon. The larger antimony nucleus has higher spin than phosphorus. So, in a magnetic field, it has not just two basic states but eight, ranging from pointing in the same direction as the field to pointing in the opposite direction.

In addition, the distribution of electric charge within the nucleus isn’t uniform, with more charge around the poles than the equator. That uneven charge distribution gives experimenters another handle on the nucleus in addition to its spin and magnetism. They can grab it with an oscillating electric field and controllably ease it from one spin state to another or into combinations of any two. All it takes is applying an electric field of the right frequency with a simple electrode, the researchers report.

The researchers discovered the effect by accident, Morello says. For reasons that have nothing to do with quantum computing, they had wanted to study how the antimony nucleus embedded in a silicon chip would react to jolts of the oscillating magnetic field generated by a wire on the chip. But the wire melted and broke, turning the current-carrying wire into a charge-collecting electrode that instead generated an oscillating electric field.

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Scientists have accidentally solved a decades-old quantum puzzle that could lead to new breakthroughs in entirely different kinds of computers. The breakthrough discovery not only solves a mystery that has perplexed scientists for more than half a century, but could allow researchers new capabilities when they are building quantum computers and sensors. It means that.

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Scientists in Australia have developed a new approach to reducing the errors that plague experimental quantum computers; a step that could remove a critical roadblock preventing them scaling up to full working machines.

By taking advantage of the infinite geometric space of a particular quantum system made up of bosons, the researchers, led by Dr. Arne Grimsmo from the University of Sydney, have developed quantum correction codes that should reduce the number of physical quantum switches, or qubits, required to scale up these machines to a useful size.

“The beauty of these codes is they are ‘platform agnostic’ and can be developed to work with a wide range of quantum hardware systems,” Dr. Grimsmo said.

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