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Reliable qubits are difficult to engineer. What can we do with just a few of them? Here are some ideas:

April 12, 2017 - 11:00am
Ben Reichardt
U. Southern California
1. Memory/dimensionality test.  An n-qubit system has 2^n dimensions---a big reason for quantum computers' exponential power!  But systems with just polynomial(n) dimensions can look like they have n qubits.  We give a test for verifying that your system really has 2^n dimensions.  
2. Entanglement test.  A Bell-inequality violation establishes that your systems share some entanglement (i.e., there's no classical explanation).  We give a test to show that your systems share lots of entanglement.  
3. Extended Einstein-Podolsky-Rosen (EPR) test.  Classical hidden variables can't explain a Bell inequality violation, but another non-quantum theory could explain it: non-signaling correlations like the Popescu-Rohrlich nonlocal box.  We give a test, using three spacelike-separated devices, to eliminate non-signaling explanations.  
4. Error correction test.  Error correction will be needed for scalable quantum computers.  But high qubit overhead makes it impractical for small devices.  We show that a 7-qubit computer can fault tolerantly correct errors on one encoded qubit, and that a 17-qubit computer can protect and compute fault tolerantly on seven encoded qubits.  
Atlantic 3100A

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