“ Anyone who can contemplate quantum mechanics without getting dizzy hasn ’ t understood it. ” --Niels Bohr. The Quantum Information Revolution Paul Kwiat. DARPA. Kwiat’s Quantum Clan (2012) Graduate Students: Rebecca Holmes Aditya Sharma Trent Graham Brad Christensen
“Anyone who can contemplate quantum mechanics without getting dizzy hasn’t understood it.”
Clan (2012)Graduate Students:
Jia Jun (“JJ”) Wong
Visit Prof: Hee Su Park
Quantum Information Science
Simulating other quantum
Ultimate control over
Secure key distribution
the classical limit
Measurements on quantum
Unravel the mysteries of the universe…
very big (e.g., “quantum leap”)
an unsplittable parcel/bundle of energy
a cool buzzword to get more funding, more papers, more people at your Sat. am physics lecture, etc.
all of the above
6.6 x 10-34J-s
Power output: P = (# photons/sec) x Ephoton
How do we reconcile this notion that light comes in ‘packets’ with our view of an electromagnetic wave, e.g., from a laser??
Partially transmitting mirror
How many photons per second are emitted from a 1-mW laser (l=635nm)?
3 x 1015 photons/sec =
This is an incredibly huge number – your eye basically cannot resolve this many individual photons (though the rods can detect single photons!).
And you MAY be able to see just one photon!!
A. Rose, J. Opt. Sci. Am. 43, 715 (1953)
Photon only detected in one output.
Equally likely to be transmitted or reflected –cannot tell which.
"God does not play dice with the universe."
“It seems to me that the idea of a personal God is an anthropological concept which I cannot take seriously.”
Waves add up:
1675: Newton “proved” the light was made of “corpuscles”
1818: French Academy science contest
Conclusion (at the time): Light must be a wave, since particles don’t interfere!
Mach-Zehnder: Michelson :
The solution…(Elitzur & Vaidman, 1993)Use dual wave-particle nature of quantum objects (“wavicles”)
Single photon always shows up at D1(complete destructive interference to D2)
50% chance that photon is absorbed by object50% chance it isn’t 25% chance D2 fires “interaction-free measurement” of object
Quantum Cryptography = Quantum Key Distribution
Polarization: --the oscillation direction of the light
--property of each photon
--can measure with polarizers, calcite, etc.
Prob(horizontally polarized photon pass horizontal polarizer): 1
Prob(horizontally polarized photon pass vertical polarizer): 0
Prob(diagonally pol. photon pass horizontal polarizer): 1/2
Prob(diagonally pol. photon pass vertical polarizer): 1/2
high energy parent photon can split into two daughter photons
(with same polarization)
We don’t know WHICH crystal created the pair of photons, but we know they both came from the same crystal they MUST have the same polarization.
Last week news item: they used the entangled photons to teleport the state of a photon between the islands – world distance record for quantum teleportation!
Since we can seemingly “see” without “looking” using quantum interrogation, does this mean an eavesdropper could use it to defeat quantum cryptography?
No! It turns out that even making the gentlest measurement possible, if the eavesdropper gains any information, she disturbs the state.
Or if she is so gentle so as not to disturb the state, then she gets no information.
Quantum key distribution is secure against any attack allowed by the laws of physics!
(Bardeen, Brattain & Shockley, 1947)
~100 million transistors
Size of an atom
Physical realization of qubits any 2 level system
2-level atom: ge
All 2-level systems are created equal, but some are more equal than others!
Quantum communication photons
Quantum storage atoms, spins
Scaleable circuits superconducting systems
Intrinsic randomness in measurement
“Entanglement”, and the scaling that results, is the key to the power of quantum computing.
, information is stored in a bit register: a 3-bit
register can store
number, from 0 – 7.
Quantum Mechanically, a register of 3 entangled qubits can store all of these numbers in superposition:
one N-bit number
(all possible) N-bit numbers
register can simultaneously store
2300 ~ 1090 numbers
1,000,000,000,000,000,000, 000,000,000,000,000,000, 000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000,000
This is more than the total number of particles in the Universe!
Some important problems benefit from this exponential scaling, enabling solutions of otherwise insoluble problems.
For example, it is hard to factor 167,659
But an elementary school student can easily multiply389 x 431 = 167,659
This asymmetry in the difficulty of factoring vs. multiplying is the basis of public key encryption, on which everything from on-line transaction security to ensuring diplomatic secrecy depends.
Quantum algorithms enable one to factor numbers into their prime constituents MUCH faster:
The difficulty (impossibility) of factoring large numbers (and the ease of creating a large number from its factors) is the basis of public key encryption (which nearly everyone uses for secure transmission today).
shorthand “wave function”
Probability of measuring , P = ||2
Probability of measuring , P= ||2
|rest + |moving
Collective motion: the “quantum data bus”
state of motion
|0 + |1
Quantum Computing Explored
Sep 12 2001 @ 08:10
American computer scientists are studying the possibility to build a super fast computer based on quantum physics.
Need WEAK coupling to environment to avoid decoherence, but you also need STRONG coupling to at least some external modes in order to ensure high speed and reliability.
The unlikely – impossible?
0 5 10 ~15 20? 25??
The as yet unimagined!!!
Games & Toys
# of instructions
Classical ~ eAL
~ 1017 instructions: 8 months
~ 109 operations: seconds
# of bits, L, factored