LESSON 6. Quantum computers. Unreal

Part I

Reading and Speaking

Discuss the following with a partner.

1. What do you know about quantum computers?

2. What fields could they be used in?

3. When will they become commercially available?

Read the text.

Magical Theories

Everything we know is consistent with the possibility that quantum computers are the end of the line—that is, that they are the most general kind of computer compatible with the laws of physics. But physicists do not yet have a final theory of physics, so one cannot rule out the possibility that someday a future theory might reveal a physical means to solve the problems that seem unsolvable today. As you would expect, people speculate about yet more powerful kinds of computers, some of which would make quantum computers look as pedestrian as vending machines.

All of them, however, would rely on speculative changes to the laws of physics. One of the central features of quantum mechanics is a mathematical property called linearity. In 1998 Daniel S. Abrams and Seth Lloyd, both then at M.I.T., showed that if a small nonlinear term is added to the equations of quantum mechanics, quantum computers would be able to efficiently solve NP-complete problems - a particularly difficult set of mathematical challenges, which even the best existing computers cannot solve quickly. Before you get too excited, you should realize that if such a nonlinear term existed, then one could also violate Heisenberg’s uncertainty principle and send signals faster than the speed of light. As Abrams and Lloyd pointed out, perhaps the best interpretation of these results is that they help to explain why quantum mechanics is linear.

Another speculative type of machine would achieve extravagant computational abilities by cramming an infinite number of steps into a finite time. Unfortunately, according to physicists’ current understanding, time seems to degenerate into a sea of quantum fluctuations— something like a foam instead of a uniform smooth line—on the scale of 10–43 second (the Planck time), which would seem to make this kind of machine impossible.

If time cannot be sliced with arbitrary thinness, then perhaps another way to solve NP complete problems efficiently would be to exploit time travel. Physicists studying the issue talk not about time machines but about closed timelike curves (CTCs). In essence a CTC is a route through space and time that matter or energy could travel along to meet up with itself in the past, forming a closed loop. Current physical theory is inconclusive on whether CTCs can exist, but that need not stop us from asking what the consequences would be for computer science if they did exist.

Skim the text and answer the questions.

1. Can we currently build devices more powerful than quantum computers? If yes, why? If no, why not?
2. What did Daniel S. Abrams and Seth Lloyd show in 1998?
3. What particularly difficult set of mathematical problems is discussed in the text?
4. What does Heisenberg’s uncertainty principle state?
5. What is a CTC?

Say whether the statements are true or false.

1. Quantum computers are the most general kind of computer compatible with the laws of physics.
2. Scientists have a final theory of physics.
3. There exists a nonlinear term that enables to violate Heisenberg’s uncertainty principle and send signals faster than the speed of light.
4. According to physicists’ current understanding, time seems to degenerate into a sea of quantum fluctuations.
5. Physicists can efficiently solve NP complete problems through time travel.

5. Summarize the text. Structure your speech using the words:

· First\Then\Finally + noun + verb…

· The author\ text also\further describes + noun

· The text\author states that + clause

· The first\second paragraph discusses + noun

Part II

Unreal situations

Useful information

To show that the situations are unreal we can use:

- Modal verbs

- The Complex Subject

- Verb 'wish'

Modal verbs

1. Skim text “Magical Theories” and answer the questions.

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