Quantum world record smashed

TEST YOURSELF

A normally fragile quantum state has been shown to survive at room temperature for a world record 39 minutes.

(1) An international team including Stephanie Simmons of Oxford University, report in this week's Science a test performed by Mike Thewalt of Simon Fraser University, Canada, and colleagues. In conventional computers data is stored as a string of 1s and 0s. In the experiment quantum bits of information, 'qubits', were put into a 'superposition' state in which they can be both 1s and 0 at the same time – enabling them to perform multiple calculations simultaneously.

(2) In the experiment the team raised the temperature of a system, in which information is encoded in the nuclei of phosphorus atoms in silicon, from ‑269 °C to 25 °C and demonstrated that the superposition states survived at this balmy temperature for 39 minutes. The team even found that they could manipulate the qubits as the temperature of the system rose, and that they were robust enough for this information to survive being 'refrozen' (the optical technique used to read the qubits only works at very low temperatures).

(3) '39 minutes may not seem very long but as it only takes one-hundred-thousandth of a second to flip the nuclear spin of a phosphorus ion – the type of operation used to run quantum calculations – in theory over 20 million operations could be applied in the time it takes for the superposition to naturally decay by one percent. Having such robust, as well as long-lived, qubits could prove very helpful for anyone trying to build a quantum computer,' said Stephanie Simmons. 'This opens up the possibility of truly long-term coherent information storage at room temperature,' said Mike Thewalt of Simon Fraser University.

(4) The team began with a sliver of silicon doped with small amounts of other elements, including phosphorus. Quantum information was encoded in the nuclei of the phosphorus atoms: each nucleus has an intrinsic quantum property called 'spin', which acts like a tiny bar magnet when placed in a magnetic field. Spins can be manipulated to point up (0), down (1), or any angle in between, representing a superposition of the two other states. The team prepared their sample at just 4 °C above absolute zero (‑269 °C) and placed it in a magnetic field. Additional magnetic field pulses were used to tilt the direction of the nuclear spin and create the superposition states. When the sample was held at this cryogenic temperature, the nuclear spins of about 37 per cent of the ions remained in their superposition state for three hours. The same fraction survived for 39 minutes when the temperature of the system was raised to 25 °C.

(5) 'These lifetimes are at least ten times longer than those measured in previous experiments,' said Stephanie Simmons. 'We've managed to identify a system that seems to have basically no noise. They're high-performance qubits.' There is still some work ahead before the team can carry out large-scale quantum computations. The nuclear spins of the 10 billion or so phosphorus ions used in this experiment were all placed in the same quantum state. To run calculations, however, physicists will need to place different qubits in different states.

I. Read the text. Choose the most suitable heading from the list (A‑G) for each part (1‑5) of the text. There are two extra headings you do not need to use.

A. Long-range outlook

B. Coming challenges

C. A magnetic field method

D. Temperature matters

E. Uncertain results

F. The essence of the experiment

G. The procedure

II. Read the text. For statements (6‑15) choose “True” if the statement is true according to the text, “False” if the statement is false.

6. The experiment was performed by Stephanie Simmons of Oxford University and her team.

7. The superposition quantum bits are supposed to function either as 1s or 0 at the same time.

8. The experiment was carried out at the temperature range between nearly absolute zero and room temperature.

9. Earlier optical equipment worked at low temperatures only.

10. Ms. Simmons supposed that a quantum computer can become a really good information storage in future.

11. Phosphorus was excluded from the sample’s enveloping cover.

12. Having been made the sample was placed in a magnetic field.

13. Superpositional state was promoted by extra magnetism.

14. Nuclear spins preserve their superpositional state at room temperature nearly 4,5 times as shorter as at absolute zero.

15. The researchers will place qubits in different states in order to avoid calculations.

III. Read the text. For questions (16‑20) choose the correct answer (A, B, C or D).

16. The quantum state, which is normally easily destroyed, _____

A. has reached its maximum point.

B. has lasted its longest period at room temperature.

C. is constant at very low temperatures.

D. has been researched during 39 minutes.

17. The superpositional state could be manipulated _____

A. easier, the higher the temperature is.

B. as the system enlarged.

C. when the system’s temperature remained frozen.

D. with the temperature increase.

18. Long-lived qubits can help _____

A. the developers of quantum computers.

B. the natural decay by 1 %.

C. the researchers of Simon Fraser University.

D. rearranging informational starage.

19. ‘Spin’ is a peculiar property of a nucleus _____

A. when placing it in a magnetic field.

B. which manipulates the superposition.

C. that represents the type of an element.

D. which can perform as a magnet.

20. Recent results have shown that _____

A. large-scale computer calculations are imaginary.

B. experiments were not noisy at all.

C. superpositional states can last ten times longer.

D. about one third of ions remained in their superposition on heating.

IV. Match the words (21‑30) with their definitions (a‑l). There are two definitions that you do not need to use.

21.	fragile	a.	the positively charged central core of an atom
22.	superposition	b.	plain, basic, or uncomplicated in form, nature, or design
23.	simultaneously	c.	forming a unified whole
24.	nucleus	d.	the principle by which the description of the state of a physical system can be broken down into descriptions that are themselves possible states of the system.
25.	to survive	e.	a mathematical determination of the amount or number of something
26.	calculation	f.	easily broken or damaged
27.	coherent	g.	establish or indicate
28.	sample	h.	a stable subatomic particle with a positive electric charge equal in magnitude to that of an electron
29.	fraction	i.	a small part or quantity intended to show what the whole is like
30.	to identify	j.	a small or tiny part, amount, or proportion of something
		k.	at the same time
		l.	continue to live or exist

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