Week 2, summary
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1. quantum gates: 
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   Unitary matrices. 
   Connection between unitary gates and Schrodinger's equation. 
   Examples for quantum gates: Not, Hadamard, Controlled Not. 
   A quantum array of gates creating Bell states. 
   Quantum Teleportation. 

2. Quantum circuits:
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   N qubit systems. Tensor product revisited more rigorously.
   Definition of Quantum circuits.

3. Universal gates: 
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   Approximating unitary matrices. 
   Definition of universal sets of gates. 
   Examples for universal sets of gates. 
   Discussion about translating between different sets of gates.  
   A proof that it suffices to approximate 
   each gate to within order 1 over the number of gates, using a 
   hybrid argument. Statement of 
   Solovay Kitaev theorem, showing that universal gates approximate 
   other gates on a constant number of qubits exponentially fast.