量子计算的重要性

Why does quantum computing matter?

Computing technology is advancing at a truly stunning pace. Three decades ago, the 80486 processor allowed users to execute 50 MIPS (million instructions per second). Today, small computers like the Raspberry Pi can reach 5,000 MIPS, while desktop processors can easily reach 50,000 to 300,000 MIPS. If we have an exceptionally difficult computational problem we’d like to solve, a very reasonable strategy is to simply wait for the next generation of processors to make our lives easier, our videos stream faster, and our games more colorful.

For many problems that we care about, however, we’re not so lucky. We might hope that getting a CPU that’s twice as fast will let us solve problems that are twice as big, but as with so much in life, “more is different.” Suppose we sort a list of 10 million numbers and find that it takes about 1 second. Later, if we want to sort a list of 1 billion numbers in 1 second, we’ll need a CPU that’s 130 times faster, not just 100 times. When solving some kinds of problems, this gets even worse: for some graphics problems, going from 10 million to 1 billion points would take 13,000 times longer.

Problems as widely varied as routing traffic in a city and predicting chemical reactions become more difficult much more quickly. If quantum computing was about making a computer that runs 1,000 times as fast, we would barely make a dent in the daunting challenges that we want to solve. Fortunately, quantum computers are much more interesting. We expect that quantum computers will be much slower than classical computers but that the resources required to solve many problems will scale differently, such that if we look at the right kinds of problems, we can break through “more is different.” At the same time, quantum computers aren’t a magic bullet—some problems will remain hard. For example, while it is likely that quantum computers can help us immensely with predicting chemical reactions, they may not be much help with other difficult problems.

Investigating exactly which problems we can obtain such an advantage in and developing quantum algorithms to do so has been a large focus of quantum computing research. Up until this point, it has been very difficult to assess quantum approaches this way, as doing so required extensive mathematical skill to write out quantum algorithms and understand all the subtleties of quantum mechanics.

As industry has started developing platforms to help connect developers to quantum computing, however, this situation has begun to change. By using Microsoft’s entire Quantum Development Kit, we can abstract away most of the mathematical complexities of quantum computing and begin actually understanding and using quantum computers. The tools and techniques taught in this book allow developers to explore and understand what writing programs for this new hardware platform will be like.

Put differently, quantum computing is not going away, so understanding what problems we can solve with it matters quite a lot indeed! Independent of whether a quantum “revolution” happens, quantum computing has factored—and will continue to factor—heavily into decisions about how to develop computing resources over the next several decades. Decisions like these are strongly impacted by quantum computing:

• What assumptions are reasonable in information security?
• What skills are useful in degree programs?
• How can we evaluate the market for computing solutions?

For those of us working in tech or related fields, we increasingly must make such decisions or provide input for them. We have a responsibility to understand what quantum computing is and, perhaps more important, what it is not. That way, we will be best prepared to step up and contribute to these new efforts and decisions.

All that aside, another reason quantum computing is such a fascinating topic is that it is both similar to and very different from classical computing. Understanding both the similarities and differences between classical and quantum computing helps us understand what is fundamental about computing in general. Both classical and quantum computation arise from different descriptions of physical laws such that understanding computation can help us understand the universe in a new way.

What’s absolutely critical, though, is that there is no one right or even best reason to be interested in quantum computing. Whatever brings you to quantum computing research or applications, you’ll learn something interesting along the way.