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Weinstein Y.S.,MITRE Inc
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We explore the implementation of pseudorandom single-qubit rotations and multiqubit pseudorandom circuits constructed only from Clifford gates and the T gate, a phase rotation of π/4. Such a gate set would be appropriate for computations performed in a fault tolerant setting. For single-qubit rotations the distribution of parameters found for unitaries constructed from Clifford plus T quickly approaches that of random rotations and requires significantly fewer gates than the construction of arbitrary single-qubit rotations. For Clifford-plus-T pseudorandom circuits we find an exponential convergence to a random matrix element distribution and a Gaussian convergence to the higher-order moments of the matrix element distribution. In addition, the nearest-neighbor eigenangle statistics distribution almost immediately converges to that of random unitary matrices. All of these convergence rates are found to be insensitive to the number of qubits. © 2013 American Physical Society.


Weinstein Y.S.,MITRE Inc
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We simulate the implementation of a T gate, or π8 gate, for a [7,1,3] encoded logical qubit in a nonequiprobable error environment. We demonstrate that the use of certain non-fault-tolerant methods in the implementation may nevertheless enable reliable quantum computation while reducing basic resource consumption. Reliability is determined by calculating gate fidelities for the one-qubit logical gate. Specifically, we show that despite using a non-fault-tolerant procedure in constructing a logical zero ancilla to implement the T gate, the gate fidelity of the logical gate, after perfect error correction, has no first order error terms. Meaning, any errors that may have occurred during implementation are "correctable" and fault tolerance may still be achieved. © 2013 American Physical Society.


Weinstein Y.S.,MITRE Inc
Quantum Information Processing | Year: 2011

In this paper I explore the entanglement evolution of qubits that are part of a five qubit quantum error correction code subject to various decohering environments. Specifically, I look for possible parallels between the entanglement degradation and the fidelity of the logical qubit of quantum information stored in the physical qubits. In addition, I note the possible exhibition of entanglement sudden death (ESD) due to decoherence and question whether ESD is actually a roadblock to successful quantum computation. © Springer Science+Business Media, LLC 2010.


Weinstein Y.S.,MITRE Inc
Quantum Information Processing | Year: 2015

Quantum error correction (QEC) entails the encoding of quantum information into a QEC code space, measuring error syndromes to properly locate and identify errors, and, if necessary, applying a proper recovery operation. Here we compare three syndrome measurement protocols for the [[7,1,3]] QEC code: Shor states, Steane states, and one ancilla qubit by simulating the implementation of 50 logical gates with the syndrome measurements interspersed between the gates at different intervals. We then compare the fidelities for the different syndrome measurement types. Our simulations show that the optimal syndrome measurement strategy is generally not to apply syndrome measurements after every gate but depends on the details of the error environment. Our simulations also allow a quantum computer programmer to weigh computational accuracy versus resource consumption (time and number of qubits) for a particular error environment. In addition, we show that applying syndrome measurements that are unnecessary from the standpoint of quantum fault tolerance may be helpful in achieving better accuracy or in lowering resource consumption. Finally, our simulations demonstrate that the single-qubit non-fault-tolerant syndrome measurement strategy achieves comparable fidelity to those that are fault tolerant. © 2015, Springer Science+Business Media New York.


Weinstein Y.S.,MITRE Inc
Journal of Modern Optics | Year: 2011

The ability to construct large photonic cluster states capable of supporting universal quantum computation relies on fusing together cluster primitives. These fusion operations are probabilistic and the efficiency of the construction process relies on recycling remains of cluster primitives that have undergone failed fusion attempts. Here I consider the effects of the inevitable decoherence that must arise while storing cluster primitives. First, I explore the case where dephased two-qubit cluster states are the basic resource for the construction of all larger cluster states, all fusion operations are successful, and no further dephasing occurs during the construction process. This allows us to explore how decoherence of the most basic, primitive clusters translates into imperfections of the larger cluster states constructed from them. I then assume that decoherence occurs before every attempted fusion operation and determine the best way to build a five-qubit cluster. This requires including the effects of the fusion operation failures. Fidelity is used as the measure of accuracy for the constructed cluster states. Finally, I include a short discussion of photon loss and how it affects the construction of simple photonic clusters. © 2011 Taylor & Francis.

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