When You're a Ket
by Prof. Paul Halpern,
University of the Sciences in Philadelphia

Tune: "When You're a Jet " (aka "Jet Song"),
from "West Side Story" by Leonard Bernstein)

Click here to play tune in the background

When you’re a ket
You’re a ket all the way
From a simple singlet
To a Spin 2 array
When you’re a ket
You’ve got brothers in place
You belong to a set
Of a complete Hilbert space
You’re never alone
You’ve always got a bra state
Proud columns you roam
Not rows- that lie prostrate
Even when you rotate
If you’re a ket
In the basis of | p >
Or the basis of | x >
Doesn’t matter to me
If you’re a ket
You are well normalized
You’re as free as you get
In a box, well or slice

You’re never afraid
Of projection operators
If they single you out
To try- and negate ya
You can pop back later
Now here’s a vignette
From- great Albert’s past
Never believed in these rules
Never thought they could last
But when you’re a ket
You can change your own fate
Just a roll of the dice
You’re a new quantum state
If EPR’s true
You’ve got instant communication
A flip of your spin
All your pals in syncopation
Will do quick rotations
And then you are set
With your own special Psi
That you’ll never forget
Til your probability’s nigh
On a ket you can rely!

Paul Halpern is the author of many books about physics and astronomy aimed at general audiences, some of which are shown below. Click on any of the covers to find out more, or to purchase from amazon.com:

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The "bra-ket" notation was invented in 1930 by Paul Dirac. The "ket", for example |B>, represents the state of a quantum system. A "bra" is a "Hermitian adjoint" of a ket (e.g. <A| is the bra version of the ket |A>). The bra version basically means the same thing as the ket version, but is expressed mathematically in a way that allows us to take an inner product, e.g. <A|B>. This gives the probability amplitude for a particle in the state |B> to transition to the state |A>. The somewhat silly terminology of putting together a "bra", such as <A|, with a "ket", such as |B>, to form a "bra-ket" or "bracket", <A|B> is proof that physicists do have a sense of humor!


The tune for this song is from Leonard Bernstein's "West Side Story". Click here to purchase the soundtrack from amazon.com.

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