Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N36: Quantum Software and Compilers: Optimization and Program SynthesisFocus Recordings Available

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Sponsoring Units: DQI Chair: Alexandru Paler, Aalto University Room: McCormick Place W194A 
Wednesday, March 16, 2022 11:30AM  11:42AM 
N36.00001: Topology Aware Unitary Synthesis for Scalable Quantum Circuit Optimization Mathias T Weiden, Justin Kalloor, Tirthak Patel, Ed Younis, Costin C Iancu, John D Kubiatowicz Unitary synthesis is an optimization technique that can achieve optimal multiqubit gate counts for many classes of quantum circuits, but is ultimately limited in scalability by its exponential memory requirements. Applying unitary synthesis to large width quantum circuits requires divideandconquer partitioning of circuits into smaller components that can be directly optimized. In this talk, we will present features of the scalable synthesis BQSKit toolkit that enable the optimization of circuits with hundreds of qubits. We will examine the tradeoffs for different partitioning techniques and discuss what parameters of partitioned subcircuits most influence synthesis performance. We will additionally explore the impact of physical qubit topology on the multiqubit gate count of synthesized circuits. Finally, we propose a topology aware synthesis technique that partitions quantum circuits and matches subcircuits with "physical" qubit subtopologies before optimizing. We will demonstrate how this technique can be used to improve the multiqubit gate count of large width quantum circuits on realistic physical topologies. When compared with traditional quantum compilers using peephole optimization and mapping algorithms such as Qiskit, Tket or Cirq, our approach is able to provide significant circuit depth reduction with little sensitivity to the underlying physical chip topology. 
Wednesday, March 16, 2022 11:42AM  11:54AM 
N36.00002: Building DomainSpecific Compilers Using Parameterized Circuit Instantiation Ed Younis, Costin C Iancu Parameterized circuit instantiation is a common technique encountered in the generation of circuits for a large class of 
Wednesday, March 16, 2022 11:54AM  12:06PM 
N36.00003: Optimizing Quantum Circuit Synthesis for Permutations on Limited Connectivity Topologies Cynthia Chen, Helena Zhang, Bruno Schmitt, Lev S Bishop, Ali JavadiAbhari Depth optimization of permutation circuits is an important problem because permutations can be used to map any circuit onto limitedconnectivity hardware and shallower circuits take less time to execute, resulting in reduced decoherence. SAT solvers can find optimaldepth circuits, but cannot scale to large qubit numbers, and most existing depthoptimizing methods are restricted to certain topologies. We propose LeftRight Synthesis (LRSynth), the first scalable SWAPbased depthoptimizing method for synthesizing permutations on any limited connectivity topology. LRSynth is a divide and conquer approach that partitions the topology into two halves and moves qubits to the correct half using matchings. Its recursive nature makes it amenable for use in conjunction with exact methods to solve the small inner recursions and for parallelizing recursive calls. We benchmark LRSynth against existing depthoptimizing methods and an optimaldepth SAT solver for topologies commonly found on physical devices such as trees, rings, and grids. LRSynth scales better than SAT solvers, yet achieves closetooptimal depths and outperforms in gate count. It is applicable to any connectivity topology, while achieving comparable results to bestknown heuristics tailored to specific topologies. 
Wednesday, March 16, 2022 12:06PM  12:42PM 
N36.00004: Formal methods of quantum program analysis Invited Speaker: Matthew Amy Quantum computation is rapidly moving out of science fiction and into reality. With these growing computational devices larger and more complex quantum algorithms are increasingly being programmed, compiled, and run on a wide range of hardware. Accordingly, quantum programming languages and compilers are becoming more intricate, bringing new challenges to the scalable design and verification of quantum programs. To address these challenges, as with classical computing we need a mature ecosystem of tools for the analysis of quantum programs. In this talk, I will discuss some formal methods for the analysis of quantum programs and show how they can be used to improve the reliability of quantum compilers as well as power up circuit optimizations. 
Wednesday, March 16, 2022 12:42PM  12:54PM 
N36.00005: Rapid Quantum Compiler Prototyping through a MultiLevel Intermediate Representation Alexander J McCaskey, Thien Nguyen As quantumclassical computing architectures progress toward tighter CPUQPU integration, programmers of these novel accelerated systems will need robust and performant compiler infrastructures that map highlevel programmatic representations to a heterogeneous set of binary code and executables. Moreover, there is a desire to see tight integration with classical compiler systems in an effort to promote future coupling of classical and quantum code bases. Recently, researchers have defined a quantumclassical runtime API specification based on the LLVM intermediate representation (IR). This Quantum Intermediate Representation (QIR) provides a unified abstraction layer for language compilers as well as robust code generation utilities for available quantum computer backends and simulators. We present a compiler platform, qcor, that lowers language representations to LLVM code adherent to the QIR specification. Our approach leverages the novel MultiLevel Intermediate Representation (MLIR) framework to take a languagelevel quantum IR tree down to the QIR. We leverage this multilevel representation for pertinent quantum optimizations and circuit synthesis. Ultimately, our approach enables quick mapping of quantum language parse trees to the MLIR, which can be readily lowered to the QIR for executable generation. We will demonstrate the utility of this approach, including how it enables multiquantumlanguage integration and library development. 
Wednesday, March 16, 2022 12:54PM  1:06PM 
N36.00006: An Intel Quantum Software Development Kit for Efficient Execution of Variational Algorithms Anne Y Matsuura, Shavindra P Premaratne, XinChuan Wu, Nicolas P Sawaya, Albert T Schmitz, Pradnya Khalate, Sahar Daraeizadeh, Gian Giacomo Guerreschi, Nader Khammassi, Kevin Rasch, Xiang Zou, Justin Hogaboam Variational algorithms are some of the most promising workloads for quantum computing systems. We have developed a fullstack Intel Quantum Software Development Kit (SDK) with an LLVMbased C++ compiler and system software workflow that enables the usage of a single selfcontained source file, consisting of both the classical optimizer and the quantum program, to execute variational algorithms on a simulated qubit backend. We demonstrate the operational accuracy of this fullstack computational stack by executing a variational algorithm to generate thermofield double states [1, 2]. Our SDK automatically calculates and feeds back new variational parameters for each algorithm pass. We demonstrate excellent agreement with independently generated reference data in the case of ansatzes with both increased number of qubits and variational parameters. 
Wednesday, March 16, 2022 1:06PM  1:18PM 
N36.00007: Optimized Fermionic SWAP Networks Via HardwareAware Compilation and Equivalent Circuit Averaging for QAOA Rich Rines, Akel Hashim, Victory Omole, Ravi K Naik, John Mark Kreikebaum, David I Santiago, Frederic T Chong, Irfan Siddiqi, Pranav Gokhale Hardwareaware compilation techniques and gatebased optimizations play a key role in minimizing errors and maximizing performance of noisy intermediatescale quantum (NISQ) devices. The fermionic SWAP network is an important quantum subroutine that can be used to efficiently implement NISQ quantum applications such as the Quantum Approximate Optimization Algorithm (QAOA) on dense graphs with just a minimallyconnected qubit topology. In this work, we present lowlevel tools which further improve the performance of fermionic SWAP networks: (1) optimized gate decompositions utilizing a richer variety of hardware operations, (2) circuit compilation exploiting the degrees of freedom in each gate decomposition to maximize singlequbit gate cancellation, and (3) Equivalent Circuit Averaging (ECA), a new technique to efficiently mitigate systematic errors by averaging over equivalent circuit decompositions. These optimizations are experimentally validated on the Advanced Quantum Testbed, where we find a 60% average reduction in total variation distance for depth1 QAOA circuits executed on four superconducting transmon qubits. 
Wednesday, March 16, 2022 1:18PM  1:30PM 
N36.00008: Robust Quantum Circuit Approximation for ResourceEfficient Circuit Synthesis Tirthak Patel, Ed Younis, Costin C Iancu, Wibe A de Jong, Devesh Tiwari We present a procedure to robustly generate approximations for quantum circuits to reduce their CNOT gate count. Our approach employs circuit partitioning for scalability with procedures to 1) reduce circuit length using approximate synthesis, 2) improve fidelity by running circuits that represent key samples in the approximation space, and 3) reason about approximation upper bound. Our evaluation results indicate that our approach of "dissimilar" approximations provides close fidelity to the original circuit. Overall, the results indicate that the procedure can reduce CNOT gate count by 3080% on ideal systems and decrease the impact of noise on existing and nearfuture quantum systems. 
Wednesday, March 16, 2022 1:30PM  1:42PM 
N36.00009: Lattice Surgery Quantum Error Correction Compiler George W Watkins, Hoang M Nguyen, HoiKwan Lau, Alexandru Paler, Steven Pearce, Robert Raussendorf, Varun Seshadri, Keelan P Watkins We developed a state of the art, high performance compiler for surface code quantum error correction. Our compiler translates any quantum circuit to a faulttolerant one error corrected one that follows Lattice Surgery (LS) instructions. We offer our compiler publicly through a web interface, a web service, and as an open sourced Python package. In this talk, we will demonstrate the operation of our compiler and the web visualizer for the conversion of a sample quantum circuit. We will also discuss our results on compiling thousands of qubits, and on verifying the correctness of the compiler output. Generally, verifying the correctness is an intractable problem. An example of this will be showcased during our talk. With respect to future work, we will present our preliminary results on implementing massively parallel compilation of very large scale circuits. 
Wednesday, March 16, 2022 1:42PM  1:54PM 
N36.00010: Fullstack Quantum Compilation: Mind the Pulse Gap Yonatan Cohen, Dor Israeli, Nir Halay, Uri Abend The quantum computing ecosystem has grown substantially in terms of accessible cloud solutions, quantum programming languages, and different open source and proprietary tools. The physical and engineering effort is also rapidly advancing with new technologies and ideas being put forth on a daily basis, e.g. new qubit types, error correction algorithms, qRAM, and many more. Hence, it becomes increasingly important to bridge the gap between the various enduser interfaces and the many different types of QPUs. 
Wednesday, March 16, 2022 1:54PM  2:06PM 
N36.00011: Quantum Intermediate Representation  Why, What and How Yonatan Cohen, Itamar Sivan, Dor Israeli As the quantum computing stack evolves, it becomes increasingly important to create standard interfaces in order to create larger communities and develop a rich ecosystem. In particular, intermediate representations (IRs), which allow the standard description of quantum programs that serve as a compilation target for highlevel programming languages and as a source for execution by quantum machines, will play a critical role in the growth of the field. Here we discuss the various considerations in designing such IRs for quantum computing and how different choices may affect performance as well as ecosystem development. 
Wednesday, March 16, 2022 2:06PM  2:18PM 
N36.00012: Variational Quantum Algorithms With the Quantum Orchestration Platform Yonatan Cohen, Lior Ella, Arthur Strauss, Gal Winer Among the candidates that would showcase a nearterm potential advantage over classical computing, Variational Quantum Algorithms (VQAs) do find a large interest in the research community, for they share in common the idea to exploit quantum information processing as a tool for computing difficult functions in the frame of a wider classical computation. Therefore, there is a dire need to build a unified framework for controlling quantum processors and running heavy classical processing. The simultaneous realization of those two features constitutes an essential requirement for running efficient hybrid classicalquantum algorithms. 
Wednesday, March 16, 2022 2:18PM  2:30PM 
N36.00013: Approaching the theoretical limit in quantum gate decomposition Zoltan Zimboras, Peter Rakyta We propose a novel numerical approach to decompose general quantum programs in terms of single and twoqubit quantum gates with a CNOT gate count very close to the current theoretical lower bounds. In particular, it turns out that 15 and 63 CNOT gates are sufficient to decompose a general 3 and 4qubit unitary, respectively. This is currently the lowest achieved gate count compared to other algorithms. Our approach is based on a sequential optimization of parameters related to the singlequbit rotation gates involved in a predesigned quantum circuit used for the decomposition. In addition, the algorithm can be adopted to sparse interqubit connectivity architectures provided by current midscale quantum computers, needing only a few additional CNOT gates to be implemented in the resulting quantum circuits. 
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