Quantum state

Physicists propose way to use quantum bidding in bridge

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A team of physicists in Europe, led by Marcin Pawlowski, has proposed a way to use entangled quantum particles to improve the odds of winning in the game of bridge. As the team notes in their paper published in Physical Review X, their proposition appears to be the first example of using quantum enhancement of information transfer as it applies to a real-world (non-physics) application.

 
Entanglement is where pairs of quantum particles are generated where their quantum state is no longer defined independently—instead a quantum state comes to exist that defines them as a single unit. The team in Europe has taken this concept and applied it to the game of bridge, increasing the odds of winning by a pair of players that successfully employs the strategy they’ve devised.
Bridge is a card game played by teams of paired individuals—successful players learn to communicate meaningfully with one another to convey information each needs to improve their hand, without being specific—that’s against the rules. In this new scenario, Pawlowski, et al, suggest that in addition to a handful of cards, players are given the means to receive (and measure) one particle of an entangled pair from their mate—doing so they note, would not violate the rules of bridge as quantum entanglement cannot be used to send messages.
Use of entanglement in bridge would only come up during certain parts of play, such as when hands are dealt, and players on a team are trying to determine what cards their partner has that could be used to fill in the gaps in their own hand. Here team members would use combined measurements on the entangled particles along with information provided via coded bids to come up with partial information to help them better understand each other’s cards. Such a strategy isn’t foolproof, of course, it would help up the odds of winning rather than provide a clear path to victory. Pawlowski and his team have calculated that using their strategy would increase the probability of one team member guessing what cards their mate is holding from 87.5% to 89.5%, a 2 percent gain, but one that could for a team playing tournament style, mean a decided advantage.
Explore further: Scientists open a new window into quantum physics with superconductivity in LEDs

ABSTRACT
Quantum methods allow us to reduce communication complexity of some computational tasks, with several separated partners, beyond classical constraints. Nevertheless, experimental demonstrations of this have thus far been limited to some abstract problems, far away from real-life tasks. We show here, and demonstrate experimentally, that the power of reduction of communication complexity can be harnessed to gain an advantage in a famous, immensely popular, card game—bridge. The essence of a winning strategy in bridge is efficient communication between the partners. The rules of the game allow only a specific form of communication, of very low complexity (effectively, one has strong limitations on the number of exchanged bits). Surprisingly, our quantum technique does not violate the existing rules of the game (as there is no increase in information flow). We show that our quantum bridge auction corresponds to a biased nonlocal Clauser-Horne-Shimony-Holt game, which is equivalent to a 2→1 quantum random access code. Thus, our experiment is also a realization of such protocols. However, this correspondence is not complete, which enables the bridge players to have efficient strategies regardless of the quality of their detectors.

Quantum ‘world record’ smashed

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An artistic rendition of a 'bound exciton' quantum state used to prepare and read out the state of the qubits
Quantum systems are notoriously fickle to measure and manipulate

A fragile quantum memory state has been held stable at room temperature for a “world record” 39 minutes – overcoming a key barrier to ultrafast computers.

“Qubits” of information encoded in a silicon system persisted for almost 100 times longer than ever before.

Quantum systems are notoriously fickle to measure and manipulate, but if harnessed could transform computing.

The new benchmark was set by an international team led by Mike Thewalt of Simon Fraser University, Canada.

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“39 minutes may not seem very long. But these lifetimes are many times longer than previous experiments”

Stephanie Simmons Oxford University

“This opens the possibility of truly long-term storage of quantum information at room temperature,” said Prof Thewalt, whose achievement is detailed in the journal Science.

In conventional computers, “bits” of data are stored as a string of 1s and 0s.

But in a quantum system, “qubits” are stored in a so-called “superposition state” in which they can be both 1s and 0 at the same time – enabling them to perform multiple calculations simultaneously.

The trouble with qubits is their instability – typical devices “forget” their memories in less than a second.

There is no Guinness Book of quantum records. But unofficially, the previous best for a solid state system was 25 seconds at room temperature, or three minutes under cryogenic conditions.

In this new experiment, scientists encoded information into the nuclei of phosphorus atoms held in a sliver of purified silicon.

Magnetic field pulses were used to tilt the spin of the nuclei and create superposition states – the qubits of memory.

The team prepared the sample at -269C, close to absolute zero – the lowest temperature possible.

Artist's impression of a phosphorus atom qubit in silicon, showing a ticking clock

When they raised the system to room temperature (just above 25C) the superposition states survived for 39 minutes.

What’s more, they found they could manipulate the qubits as the temperature of the system rose and fell back towards absolute zero.

At cryogenic temperatures, their quantum memory system remained coherent for three hours.

“Having such robust, as well as long-lived, qubits could prove very helpful for anyone trying to build a quantum computer,” said co-author Stephanie Simmons of Oxford University’s department of materials.

“39 minutes may not seem very long. But these lifetimes are many times longer than previous experiments.

“We’ve managed to identify a system that seems to have basically no noise.”

However she cautions there are still many hurdles to overcome before large-scale quantum computations can be performed.

For one thing, their memory device was built with a highly purified form of silicon – free from the magnetic isotopes which interfere with the spin of nuclei.

For another, the spins of the 10 billion or so phosphorus ions used in this experiment were all placed in the same quantum state.

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“What’s most important is this is silicon. The global investment in this material means it has a lot of potential for engineering”

Dr Thaddeus Ladd HRL Laboratories

Whereas to run calculations, physicists will need to place different qubits in different states – and control how they couple and interact.

“To have them controllably talking to one another – that would address the last big remaining challenge,” said Dr Simmons.

Independent experts in the quantum field said the new record was an “exciting breakthrough” that had long been predicted.

“This result represents an important step towards realising quantum devices,” said David Awschalom, professor in Spintronics and Quantum Information, at the University of Chicago.

“However, a number of intriguing challenges still remain. For instance – will it be possible to precisely control the local electron-nuclear interaction to enable initialisation, storage, and readout of the nuclear spin states?”

The previous “world record” for a solid state quantum system at room temperature – 25 seconds – was held by Dr Thaddeus Ladd, formerly of Stanford University‘s Quantum Information Science unit, now working for HRL Laboratories.

“It’s remarkable that these coherence states could be held for so long in a measurable system – as measurement normally introduces noise,” he told BBC News.

“It’s also a nice surprise that nothing goes wrong warming up and cooling the sample again – from an experimental point of view that’s pretty remarkable.

“What is perhaps most important is that this is silicon. The global investment in this particular material means that it has a lot of potential for engineering.”