The presidents of MIT, Stanford, and Princeton have prepared a response to Larry Summers' comments. They are all scientists or engineers. Two of them are women.
It's a bit politically correct and has strange wording like "our nation will be considerably less than the sum of its parts." However, I think the main message is right. I like how the authors emphasize that we don't just want more women in science and engineering, we want to make sure that the really talented ones who are interested in science and engineering, that these people stay in the system.
12 February 2005
10 February 2005
Bob Laughlin on "Reinventing Physics"
Bob Laughlin, the 1998 Nobel Laureate in Physics, has just written an article about the future of physics. Basically, he slams particle physics and its reductionist philosophy. He claims that string theorists and cosmologists are particularly arrogant to think they have the monopoly on the secrets of the universe. He further advocates that collective behavior, as studied by condensed matter physics, will be the next frontier.
06 February 2005
Go Patriots!
Tom Brady (a Bay Area native!) and the New England Patriots take on the Philadephia Eagles tonight in the Super Bowl. Having lived near Boston, I've adopted the Patriots and Red Sox as favorite teams (along with the San Francisco 49ers, San Francisco Giants, Oakland A's, and San Jose Sharks). How fortunate for me; the Patriots and Red Sox have had astounding success in recent years.
If you haven't been to a Red Sox game at Fenway Park, I highly recommend it.
But back to the main point, go Pats!
If you haven't been to a Red Sox game at Fenway Park, I highly recommend it.
But back to the main point, go Pats!
05 February 2005
Washington Post article about women in physics
To get some perspective on Larry Summer's comments, the Washington Post asked Professor Meg Urry to write an article about women in physics. She's a tenured professor in the Yale astronomy and physics departments.
The article relates Urry's personal experiences with discrimination throughout her academic career. The article is well-worth reading. The other articles I have read on this topic have always been rather vague and abstract whereas Urry's writing is very personal and eye-opening.
The article relates Urry's personal experiences with discrimination throughout her academic career. The article is well-worth reading. The other articles I have read on this topic have always been rather vague and abstract whereas Urry's writing is very personal and eye-opening.
04 February 2005
Sophistication in the English language
A fellow graduate student and I were discussing the following topic during dinner. Why has English writing become less varied and sophisticated with time? Even the everyday literate person in the 1880s or supposedly even the 1960s could write better than today's American college graduates. Our vocabulary has diminished and the length of our sentences has shrunk. The graduate student I was speaking with claimed that she was told in Britain that one should only use words with Anglo-Saxon roots and not words with Latin roots. Yet there are many words in each system that have no duplicate (in connotation) in the other system. It's not just that our present day vocabulary is smaller; the way we use it is also less sophisticated. I sometimes have to re-read passages in Victorian novels because the sentences are far longer and convey so much meaning. I've also been told that biology students who have read articles from the 60s are struck by their clarity and elegance.
My graduate student friend argued that society has an obligation to educate its citizens in the better usage of language. If journalism and media raised their standards, everyday people would, too. Even in the academy, both of us have been told to use the simplest language. The advice makes some sense in science where articles are read by an international audience. However, it is strange that this tenet holds in humanities culture as well.
Perhaps I will make it my goal to write science beautifully.
My graduate student friend argued that society has an obligation to educate its citizens in the better usage of language. If journalism and media raised their standards, everyday people would, too. Even in the academy, both of us have been told to use the simplest language. The advice makes some sense in science where articles are read by an international audience. However, it is strange that this tenet holds in humanities culture as well.
Perhaps I will make it my goal to write science beautifully.
31 January 2005
Jack Frost Designs
One of my fascinations in life is with snow and ice. This morning, I came across a New York Times video about a man who takes pictures of ice formations on his greenhouse windows.
29 January 2005
New URL
I've moved the blog from qmengineer.blogspot.com to qmechanic.blogspot.com.
I originally wanted qmechanic when I started this blog. Now it's available so I'm making the switch.
I originally wanted qmechanic when I started this blog. Now it's available so I'm making the switch.
Parental blogging
The New York Times today has an article describing parents who blog about their infant children.
Of all the blogs mentioned, my favorite was "The Trixie Update", complete with graphs of the baby's projected growth and detailed explanations of milk feeding.
I think parental blogging is a rather nice addition to the blogging world as opposed to say, diaries of one's sexual exploits.
Of all the blogs mentioned, my favorite was "The Trixie Update", complete with graphs of the baby's projected growth and detailed explanations of milk feeding.
I think parental blogging is a rather nice addition to the blogging world as opposed to say, diaries of one's sexual exploits.
28 January 2005
Title of this blog
To my loyal readers,
I am trying to come up with a new title for my blog. Here are some ideas:
I am trying to come up with a new title for my blog. Here are some ideas:
- One path of a quantum mechanical engineer
- Qmechanic's picture
- Life, quantum mechanics, and all that
- Learning to love the uncertainty
and the original title: "Some thoughts from a quantum mechanical engineer."
Please let me know what you think and/or give me your favorite idea.
- qmechanic
Additional note added 5 February 2005:
Amoebe thought my ideas were lame, so I have came up with the accurate but unexciting title above.
What is a quantum computer?
Let me first explain how a "classical" computer works. The main components of a classical computer are the CPU (central processing unit), memory (in a modern computer, the RAM and hard drive), and the software. Of course, you usually have user input and output devices (e.g. keyboard, monitor), but they are just for communication with the computer and not central to the computing process itself. The software contains lines of "code" which are written instructions for the CPU to execute. For example, one instruction might be for the CPU to add the numbers 5 and 6. Another instruction could be to save the number 15 in memory. How is the memory implemented? Well, the information is saved in bits. Each bit can be in the state 0 or 1. Physically, a bit is usually implemented by placing a certain electrical charge on a capacitor (two small metal plates very close to each other). The voltage on the capacitor will then depend on how much charge is on it. If the voltage is between say 0 and 0.5 volts then we identify that state as 0 and if the voltage is greater than 0.5 volts, then that state is 1. We can change the state of the bit by moving charge on and off the capacitor.
In the last ten years, scientists have become interested in studying quantum computers. There are several reasons. First, we know that there are limits to how much classical computer power we can pack into a given volume. The rise of the computing age has been spurred by the fact that semiconductor companies can squeeze more and more circuits into smaller and smaller chips with each passing year. Computers that used to fill rooms (40 - 50 years ago) now fit into 5 pound packages. However, we know from fundamental physics principles that this trend cannot continue. After all, you can't make a circuit out of one atom! So one motivation is that to continue increasing our computing power, we will have to look into alternative approaches from silicon-based classical computers. One of these is quantum computation.
Second, it appears that quantum computers can calculate some things "faster" than classical computers. What do I mean by faster? An algorithm is a set of instructions that when executed perform a useful task (like putting a bunch of words in alphabetical order or multiplying two numbers). Computer scientists measure the speed of the algorithm by comparing how many instructions have to be executed (i.e. the number of steps) and the size of the input data. For example, if the algorithm is to multiply two numbers, the size of the input data would be the total number of digits in the two numbers. In 1994, Peter Shor discovered that if you have a N-digit number that is the product of two prime factors, a quantum computer can find the factors in approximately N squared steps. In comparison, the best known algorithm for classical computers needs exp(N^(1/3)) steps. So the quantum algorithm is exponentially faster than the classical algorithm. It happens that modern encryption of data depends on the fact that it takes a classical computer exponentially increasing time to find the two prime factors. If a quantum computer could be built, it could conceivably break all the encryption codes at banks, the CIA, etc.!
Now that I've explained why quantum computers are interesting, I will try to explain how they work. A quantum computer has all the same elements as a classical computer: CPU, memory, software. The distinction is in the implementation of these elements. Recall that a classical computer saves information in bits, which can be in the state 0 or 1. A quantum computer, however, stores information in quantum bits ("qubits") that can be in both 0 and 1 at the same time. To be more precise, the most general state of a qubit is
|psi> = |state 0> + |state 1> * exp(i*phi) .
Here exp(i*phi) is a complex number whose absolute value is one and phi is a continuous number between 0 and 2*pi. Notice that I've put the words "state 0" inside "|>". This notation emphasizes that these states are no longer classical objects (like voltages on capacitors), but they are quantum states. This is a difficult concept to explain without a course in quantum mechanics, so I will merely try to give you a flavor of the idea. If we tried to put a classical bit in both states 0 and 1 at the same time, it wouldn't work. For instance, if we added 0.3 volts (the capacitor in state 0) to 0.7 volte (the capacitor in state 1), we would get 1 volt which the CPU would read at state 1. However, for a qubit, we can perform an operation on the quantum state |psi> and this operation would be performed independently on state 0 and state 1 at the same time. It's as if we are performing a computation on one classical bit that is in state 0 and on a separate classical bit that is in state 1. So we already have double the computing power! If we have N qubits, then we can perform computations on 2^N different states at the same time.
The bad news is that we can only read the result from one of these 2^N states. This is a consequence of a fundamental postulate in quantum mechanics. Therefore, we have to design very clever quantum algorithms that somehow focus all the information into one state, the state that we read out. So far besides the prime factoring algorithm, scientists have only found a handful of useful quantum algorithms which are faster than their classical counterparts.
How do we actually build these quantum computers? The key is to find a way to implement the qubit. There are many ideas so far, but the simplest is to use an ion (an electrically charged atom). If you remember your high school chemistry, you may recall pictures of an electron orbiting a nucleus. That electron can occupy different quantum states, which can be used to implement a qubit. Then you can shine a laser on the ion to move the electron from one state to another (analagous to the CPU). The problem is that if you put an electron in an excited state (as opposed to its ground state which is the most energetically favorable), then the electron will be "unhappy" and want to return to its ground state. The technical term for this behavior is "decoherence." We lose quantum information because our quantum bits interact with the environment, which causes them to relax to their most energetically favorable state. The decoherence problem has limited quantum computers to 10 qubits or less so far.
Thus quantum computers are an interesting piece of science but not yet a practical technology.
In the last ten years, scientists have become interested in studying quantum computers. There are several reasons. First, we know that there are limits to how much classical computer power we can pack into a given volume. The rise of the computing age has been spurred by the fact that semiconductor companies can squeeze more and more circuits into smaller and smaller chips with each passing year. Computers that used to fill rooms (40 - 50 years ago) now fit into 5 pound packages. However, we know from fundamental physics principles that this trend cannot continue. After all, you can't make a circuit out of one atom! So one motivation is that to continue increasing our computing power, we will have to look into alternative approaches from silicon-based classical computers. One of these is quantum computation.
Second, it appears that quantum computers can calculate some things "faster" than classical computers. What do I mean by faster? An algorithm is a set of instructions that when executed perform a useful task (like putting a bunch of words in alphabetical order or multiplying two numbers). Computer scientists measure the speed of the algorithm by comparing how many instructions have to be executed (i.e. the number of steps) and the size of the input data. For example, if the algorithm is to multiply two numbers, the size of the input data would be the total number of digits in the two numbers. In 1994, Peter Shor discovered that if you have a N-digit number that is the product of two prime factors, a quantum computer can find the factors in approximately N squared steps. In comparison, the best known algorithm for classical computers needs exp(N^(1/3)) steps. So the quantum algorithm is exponentially faster than the classical algorithm. It happens that modern encryption of data depends on the fact that it takes a classical computer exponentially increasing time to find the two prime factors. If a quantum computer could be built, it could conceivably break all the encryption codes at banks, the CIA, etc.!
Now that I've explained why quantum computers are interesting, I will try to explain how they work. A quantum computer has all the same elements as a classical computer: CPU, memory, software. The distinction is in the implementation of these elements. Recall that a classical computer saves information in bits, which can be in the state 0 or 1. A quantum computer, however, stores information in quantum bits ("qubits") that can be in both 0 and 1 at the same time. To be more precise, the most general state of a qubit is
Here exp(i*phi) is a complex number whose absolute value is one and phi is a continuous number between 0 and 2*pi. Notice that I've put the words "state 0" inside "|>". This notation emphasizes that these states are no longer classical objects (like voltages on capacitors), but they are quantum states. This is a difficult concept to explain without a course in quantum mechanics, so I will merely try to give you a flavor of the idea. If we tried to put a classical bit in both states 0 and 1 at the same time, it wouldn't work. For instance, if we added 0.3 volts (the capacitor in state 0) to 0.7 volte (the capacitor in state 1), we would get 1 volt which the CPU would read at state 1. However, for a qubit, we can perform an operation on the quantum state |psi> and this operation would be performed independently on state 0 and state 1 at the same time. It's as if we are performing a computation on one classical bit that is in state 0 and on a separate classical bit that is in state 1. So we already have double the computing power! If we have N qubits, then we can perform computations on 2^N different states at the same time.
The bad news is that we can only read the result from one of these 2^N states. This is a consequence of a fundamental postulate in quantum mechanics. Therefore, we have to design very clever quantum algorithms that somehow focus all the information into one state, the state that we read out. So far besides the prime factoring algorithm, scientists have only found a handful of useful quantum algorithms which are faster than their classical counterparts.
How do we actually build these quantum computers? The key is to find a way to implement the qubit. There are many ideas so far, but the simplest is to use an ion (an electrically charged atom). If you remember your high school chemistry, you may recall pictures of an electron orbiting a nucleus. That electron can occupy different quantum states, which can be used to implement a qubit. Then you can shine a laser on the ion to move the electron from one state to another (analagous to the CPU). The problem is that if you put an electron in an excited state (as opposed to its ground state which is the most energetically favorable), then the electron will be "unhappy" and want to return to its ground state. The technical term for this behavior is "decoherence." We lose quantum information because our quantum bits interact with the environment, which causes them to relax to their most energetically favorable state. The decoherence problem has limited quantum computers to 10 qubits or less so far.
Thus quantum computers are an interesting piece of science but not yet a practical technology.
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