AUTOMATING QUANTUM WEIRDNESS
A bowl of spaghetti or an Islamic repetitive pattern is an example of classical entanglement -- things get mixed up. And pulling one strand of spaghetti moves another strand far away. But quantum entanglement is different and difficult to express in ordinary language. When a number of particles get entangled in the quantum way, none of the particles possesses definite attributes. Only the entanglement as a whole possesses stand-alone values. Furthermore, whenever a measurement is performed on any one of the entangled particles, the state of each one of the other particles changes instantly, no matter how far it may be from its neighbors. And quantum mechanics is so delicately arranged that these instant collective changes cannot be used to signal faster-than-light. One way of expressing the entanglement situation is that Nature can communicate faster-than-light (and does so all the time). But humans cannot use entanglement to send signals because they cannot break Nature's "strong encryption" that governs the occurrence of each individual quantum jump.
Quantum entanglement is an unprecedentedly original way of getting things done in the world. Physicist Erwin Schrödinger called it "not ONE, but THE WAY, in which quantum mechanics differs most from classical expectations about how the world works."
Even at this early stage in our understanding of this phenomenon, quantum entanglement has found practical use in quantum computing, quantum cryptography and quantum teleportation as well as in many subtle new forms of optical imaging.
For the development of new quantum devices, human engineers are particularly handicapped because quantum mechanics follows a non-human logic that defies human intuition.
Enter MELVIN the robot.
Like his inventors (Mario Krenn and his colleagues at the University of Vienna), MELVIN thinks only classically. But he is able to design and test hundreds of possible thought experiments carried out with any number of quantum entangled particles. MELVIN was built to simulate the entanglement of photons. So he has at his disposal photon-entangling crystals, beam splitters, mirrors, wave plates, polarizers, holograms and perfectly efficient photon detectors. But quantum behavior is so generic, that any new results that MELVIN might discover for photons can almost certainly be exploited in other quantum systems such as electron spins, cold Bosons and superconducting junctions.
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| Schematic of MELVIN, the quantum engineer. |
The first entanglement experiments (
called EPR, after Einstein, Podolsky and Rosen whose pathbreaking 1935 paper first focused attention on the phenomenon) considered only TWO entangled particles. Work on two-particle entangled systems has been very fruitful, leading in 1964 to Bell's Non-locality Theorem, as well as the discovery of many new phenomena, notably quantum teleportation.
Entanglement was extended to THREE particles by
Greenberger, Horne and Zeilinger (GHZ) who were able (with 3 particles) to construct a particularly elegant form of Bell's Theorem.
One task of MELVIN is to search for new phenomena beyond simple EPR and GHZ experiments by expanding quantum entanglement into the realm of greater numbers of particles and into higher entanglement dimensions. "Dimensions" refers here to particular particle attributes that participate in the entanglement. MELVIN considers three different dimensions of photon entanglement: #1. Path entanglement, #2. Polarization entanglement and #3. Orbital angular momentum entanglement. Since a particular photon can be both path-entangled, polarization entangled and OAM entangled at the same time to one or more other particles, the number of different allowed kinds of entanglements rapidly becomes astronomical.
But MELVIN is up to the task. He rapidly constructs numerous virtual experiments which are tested against certain criteria set by the experimenters. Most tests fail. But those that succeed become new building blocks that increase the odds that more of the tests will succeed. MELVIN is a kind of Darwinian machine: only the fittest experiments survive. While MELVIN the robot tirelessly produces hopeful candidates, the task of the human experimenters is two-fold: #1. to devise good tests for determining the "fitness" of a proposed experiment and #2. to use human logic to simplify the fit experiments and make them as efficient as possible.
MELVIN has already produced some unusual, never-seen-before types of quantum entanglement: partial entanglements, nested entanglements, cyclic entanglements and many more. The beauty of this robot designer is that not only does MELVIN produce exotic forms of entanglement, but he also outputs an exact plan of the hardware that will produce these new entanglements in the lab.
Which leads to a third important function of the human experimenter: #3 to discover new uses, either theoretical. practical or both for the flood of new "quantum lifeforms" brought to life in the lab by this imaginative robot/human collaboration.
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| A typical experiment designed by the MELVIN/human team |
The MELVIN project is just one example of the extraordinary fruitfulness of the notion of quantum entanglement. As they say in show business: "Entanglement's got legs." It's going places.
Shri Nick predicts that either this year (2015) or the next, the Nobel Prize in physics will be awarded to
John Clauser, Alain Aspect and
Anton Zeilinger for their pioneer work in quantum entanglement. Such an award will also serve to honor the work of
John Stewart Bell whose untimely death denied him this prize.
Remember, you heard it here first.
