Quantum Architecture RG (1)

2018 21st Euromicro Conference on Digital System Design (DSD), 2018

IBM has made several quantum computers available to researchers around the world via cloud services. Two architectures with five qubits, one with 16, and one with 20 qubits are available to run experiments. The IBM architectures implement gates from the Clifford+T gate library. However, each architecture only implements a subset of the possible CNOT gates. In this paper, we show how Clifford+T circuits can efficiently be mapped into the two IBM quantum computers with 5 qubits. We further present an algorithm and a set of circuit identities that may be used to optimize the Clifford+T circuits in terms of gate count and number of levels. It is further shown that the optimized circuits can considerably reduce the gate count and number of levels and thus produce results with better fidelity.

Physical Review B, 2011

Large scale quantum computers will consist of many interacting qubits. In this paper we expand the two flux qubit coupling scheme first devised in [Phys. Rev. B 70, 140501 (2004)] and realized in [Science 314, 1427[Science 314, (2006] to a three-qubit, two-coupler scenario. We study L-shaped and lineshaped coupler geometries, and show how the interaction strength between qubits changes in terms of the couplers' dimensions. We explore two cases: the "on-state" where the interaction energy between two nearest-neighbor qubits is high, and the "off-state" where it is turned off. In both situations we study the undesirable crosstalk with the third qubit. Finally, we use the GRAPE algorithm to find efficient pulse sequences for two-qubit gates subject to our calculated physical constraints on the coupling strength.

We present a method for optimizing quantum circuits architecture. The method is based on the notion of quantum comb, which describes a circuit board in which one can insert variable subcircuits. The method allows one to efficiently address novel kinds of quantum information processing tasks, such as storing-retrieving, and cloning of channels.

Optimization of Superconducting Qubit Architectures for More Efficient Quantum Calculations

Quantum computing is one of the most fascinating advances in modern physics. The use of superconducting circuits to implement quan- tic qubits opens up extraordinary prospects. In this article, we immerse ourselves in this exciting universe in order to explain its revolutionary potential. Superconducting qubits take advantage of the unique quantum properties of certain materials to encode information with remarkable precision.

Physical Review Letters, 2008

We present a method for optimizing quantum circuits architecture. The method is based on the notion of quantum comb, which describes a circuit board in which one can insert variable subcircuits. The method allows one to efficiently address novel kinds of quantum information processing tasks, such as storing-retrieving, and cloning of channels.

Nature, 2009

By harnessing the superposition and entanglement of physical states, quantum computers could outperform their classical counterparts in solving problems of technological impact, such as factoring large numbers and searching databases 1,2 . A quantum processor executes algorithms by applying a programmable sequence of gates to an initialized register of qubits, which coherently evolves into a final state containing the result of the computation. Simultaneously meeting the conflicting requirements of long coherence, state preparation, universal gate operations, and qubit readout makes building quantum processors challenging. Few-qubit processors have already been shown in nuclear magnetic resonance 3,4,5,6 , cold ion trap 7,8 and optical 9 systems, but a solid-state realization has remained an outstanding challenge.

Proceedings of the 50th Annual International Symposium on Computer Architecture

Superconducting quantum devices are a leading technology for quantum computation, but they suffer from several challenges. Gate errors, coherence errors and a lack of connectivity all contribute to low fidelity results. In particular, connectivity restrictions enforce a gate set that requires three-qubit gates to be decomposed into one-or two-qubit gates. This substantially increases the number of two-qubit gates that need to be executed. However, many quantum devices have access to higher energy levels. We can expand the qubit abstraction of |0⟩ and |1⟩ to a ququart which has access to the |2⟩ and |3⟩ state, but with shorter coherence times. This allows for two qubits to be encoded in one ququart, enabling increased virtual connectivity between physical units from two adjacent qubits to four fully connected qubits. This connectivity scheme allows us to more efficiently execute three-qubit gates natively between two physical devices. We present direct-to-pulse implementations of several threequbit gates, synthesized via optimal control, for compilation of three-qubit gates onto a superconducting-based architecture with access to four-level devices with the first experimental demonstration of four-level ququart gates designed through optimal control. We demonstrate strategies that temporarily use higher level states to perform Toffoli gates and always use higher level states to improve fidelities for quantum circuits. We find that these methods improve expected fidelities with increases of 2x across circuit sizes using intermediate encoding, and increases of 3x for fully-encoded ququart compilation.

Quantum Information Processing, 2004

200 bit quantum computer: More states than atoms in universe! • HOWEVER: Only measure n qubits! Use only for certain algorithms (quantum simulation, factoring, optimization) 6/29/2014 Classical Computing: Factoring 2048 bit number Exponential scale up from 640 bit: 30 CPU years 10 year run time

2004

Current quantum computing hardware is unable to sustain quantum coherent operations for more than a handful of gate operations. Consequently, if near-term experimental milestones, such as synthesizing arbitrary entangled states, or performing fault-tolerant operations, are to be met, it will be necessary to minimize the number of elementary quantum gates used.