Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F37: Towards Scalable Quantum Computing ArchitecturesFocus Recordings Available

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Sponsoring Units: DQI Chair: Thaddeus Ladd, HRL Laboratories Room: McCormick Place W194B 
Tuesday, March 15, 2022 8:00AM  8:12AM 
F37.00001: Implementing symmetric entangling gates using quantum optimal control on nuclearspin qudits in ^{87}Sr atoms sivaprasad T Omanakuttan, Anupam Mitra, Michael J Martin, Ivan H Deutsch Qudits can be robustly encoded in nuclear spins of alkaline earth atoms and manipulated with magnetooptical fields. In [1], we showed that how arbitrary SU(d) singlequdit unitary maps can be implemented in such systems using quantum optimal control. We applied this in the case of the I=9/2 nuclear spin in ^{87}Sr, a d=10 dimensional qudit, through a combination of nuclear spinresonance and a tensor ACStark shift. Augmenting our toolkit with Rydberg dressing allows us to create any symmetric entangling twoqudit gate such as CPHASE. Our techniques can be used to implement a qudit entangler for qudits from d=2 to d=10 encoded in the nuclear spin using partial isometries. We also studied how decoherence due to leakage affects the creation of qudit entanglers and found that we obtain a fidelity of 0.9931, 0.9849, and 0.9674 for d=3, d=5, and d=7 respectively. This provides a powerful platform to explore the various applications of quantum information processing of qudits including metrological enhancement with qudits, quantum simulation, universal quantum computation, and quantum error correction. 
Tuesday, March 15, 2022 8:12AM  8:24AM 
F37.00002: Nonlocal Quantum Computing Theory and Spherical Time Crystals ChengHsiao Wu Four new fundamental nonlocal quantum computing operatorstate diagonal relations are derived for a model entangled atomic chain. Those relations lead directly to four interacting quasiplanar time crystals with the same Poincare cycle and the crystals are predicted to be only halfobservable. But birthanddeath of the time crystals can exist at other part of a long chain that is beyond the perpetual motion of the time crystals. Quantized condition for quantum teleportation distance is provided. The rotational symmetry breaking leads to the existence of spherical time crystals, where time axis can be curved. Quantum computing are thus rulebased and not logicgate based. That is a great departure on the starting point of quantum computing. Geometry, physical process and the nature of computing involved are triangularily related. Quantum processor, manmade or in nature, possesses intrinsic interconnection lengths just like molecular bondings. Different interconnections alter the geometry and hence the nature of computing. But generalpurpose quantum computing has to be singularly Euclidean based while the rest are not. Rules for generalpurpose (manmade), biological (where consciousness is based) and entangled atomic chain of natural phase computing are presented. 
Tuesday, March 15, 2022 8:24AM  8:36AM 
F37.00003: Scalable Distributed GateModel Quantum Computers Laszlo Gyongyosi A scalable model for a distributed quantum computation is a challenging problem due to the complexity of the problem space provided by the diversity of possible quantum systems, from smallscale quantum devices to largescale quantum computers. Here, we define a model of scalable distributed gatemodel quantum computation in nearterm quantum systems of the NISQ (noisy intermediate scale quantum) technology era. We prove that the proposed architecture can maximize an objective function of a computational problem in a distributed manner. We study the impacts of decoherence on distributed objective function evaluation. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F37.00004: Quantum optimal control for conveyormode singleelectron shuttling in Si/SiGe Alessandro David, Veit Langrock, Julian D Teske, Lars R Schreiber, Hendrik Bluhm, Tommaso Calarco, Felix Motzoi A quantum bus (QuBus) is a promising candidate for the scalability of spinqubits quantum computers. We consider a gated Si/SiGe quantum well capable of shuttling electrons smoothly by a translating confining potential (conveyormode). Dephasing coupling with valley degree of freedom and geometry of the quantum well dictate a maximum shuttling speed to keep the electron state adiabatically in the ground state and avoid excitation of the valley state. In this work we use the position of the electron as a control parameter and we optimise the trajectory of the electron to show how the electron can be shuttled faster and with lower infidelity compared to the adiabatic regime. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F37.00005: A CoDesign stararchitecture superconducting chip Hermanni Heimonen, Caspar F OckeloenKorppi, Alessandro Landra, Mario Ponce Martinez, Manuel García Pérez de Algaba, Jorge Casanova, Ines de Vega When quantum algorithms are implemented on practical quantum computers, the qubit routing problem which maps the physical qubit connectivity of the device to the qubit connectivity of the algorithm is a major hurdle. Solving the problem requires finding a pattern of SWAP gates that maps the connectivities to each other. For performing computations on NISQ devices, this problem must be solved with maximum efficiency, such that the number of SWAP gates is minimized. 
Tuesday, March 15, 2022 9:00AM  9:36AM 
F37.00006: Modular architectures for quantum computers Invited Speaker: Kenneth R Brown In this talk, I will discuss how modular quantum architectures are a promising direction for scalable quantum computers. Modules are natural building blocks that limit device complexity. In each module, the interplay of physical errors and quantum error correction will both inform the design and point to potential advatanges of heterogeneous qubit architectures. The logical connectivity between modules does not need to be geometric, and this addtional freedom enables the implementation of resourceefficient finiterate quantum error correction codes. I will conclude by discussing the stateofthe art in modular quantum computers and point to crucial next steps for achieving scalability. 
Tuesday, March 15, 2022 9:36AM  9:48AM 
F37.00007: QutritZX Calculus on superconducting transmon qutrits Shuxiang Cao, Lia Yeh, Mustafa S Bakr, Giulio Campanaro, Simone D Fasciati, James F Wills, Boris Shteynas, Vivek Chidambaram, John van de Wetering, Peter J Leek A qutritbased quantum computer requires fewer circuit components and provides more efficient ways to compose quantum circuits than a qubitbased quantum computer. QutritZX Calculus is a powerful tool for ternary quantum logic reasoning and has been shown to be helpful for qutrit logic decomposition. Here, we demonstrate the implementation of Qutrit ZXCalculus building blocks on a superconducting transmon device. We realize a single qutrit virtual Z gate and the qutrit Hadamard gate. Finally we present a twoqutrit logic gate that can be synthesized from a differential ACstark shift interaction. This work bridges the gap between the established theory of qutrit ZXCalculus and the experimental realization in superconducting quantum circuits. 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F37.00008: Universal deterministic quantum operations in microwave quantum links (Part 1) Guillermo F Peñas, Ricardo Puebla, Peter Rabl, Tomas Ramos, Juan Jose GarciaRipoll

Tuesday, March 15, 2022 10:00AM  10:12AM 
F37.00009: Universal deterministic quantum operations in microwave quantum links: Part II Ricardo Puebla, Guillermo F Peñas, Tomas Ramos, Peter Rabl, Juan Jose GarciaRipoll We present a scheme for the implementation of deterministic quantum operations in a quantum network [1]. For that, we consider a setup inspired in stateoftheart experiments based on superconducting circuits connected via microwave quantum links [2,3]. Here we propose to use quantum state transfer and photon scattering processes based on pulseshaping protocols (see part I) to implement deterministic quantum gates among distant quantum nodes without resorting to entanglement distribution or measurements. In particular, we show that a quantum gate transfer can be realized by concatenating two state transfers, while a controlledphase gate exploits the phaseimprinted in the scattered photon. In both cases we find a tradeoff between the bandwidth of the itinerant microwave photon and decoherence effects. This allows us to find optimal operation points depending on the parameters of the setup. Considering realistic qubit decay times we find gate infidelities of the order of 10^{2}. 
Tuesday, March 15, 2022 10:12AM  10:24AM 
F37.00010: Recent experimental progresses with superconducting quantum networks Youpeng Zhong Superconducting quantum circuits show great promise for building scalable quantum processors. The size of superconducting quantum processors has steadily increased from a handful to dozens of qubits over the past decade, and will likely extend to thousands of qubits over the next decade with continuous efforts in qubit integration and packaging. However, problems such as available wafer area, device yield and control wiring fanout pose serious challenges as the chip size gets bigger and bigger. A modular approach, where smaller size quantum modules are individually constructed and calibrated, then assembled into a larger architecture using quantum coherent interconnects, can circumvent these challenges and scale up superconducting quantum computers in an additive manner. In recent years, several experiments have demonstrated the deterministic quantum state transfer between two superconducting quantum modules connected by coaxial cables or waveguides[15], with fidelities ranging from ~70% to ~80%. More recent efforts using direct wirebond connection[6] or capacitive coupling[7] between the quantum modules and a coaxial cable have significantly reduced the loss, improving the state transfer fidelity to ~90%. In this talk, I will present our recent experimental progresses in this direction. 
Tuesday, March 15, 2022 10:24AM  10:36AM 
F37.00011: Bridging the Gap Between NISQ Variational Algorithms and SW/HW Architectures Constraints Yonatan Cohen, Oded Wertheim, Nikola Šibalić, Arthur Strauss, Nissim Ofek, Dor Israeli Variational algorithms are key candidate algorithms for achieving a quantum advantage in the NISQ era. Variational algorithms require close communication between classical algorithms running on a classical processor such as CPUs and quantum circuits running on a quantum processor. Efficient communication between the two, and fast reconfiguration of the quantum control sequence is key to achieving maximal utilization of quantum computation resources. 
Tuesday, March 15, 2022 10:36AM  10:48AM 
F37.00012: Universal quantum computation by quantum walks on directed graphs Ryo Asaka, Kazumitsu Sakai, Ryoko Yahagi We propose a universal quantum computation using multiparticle bosonic/fermionic quantum walks with chirality. The universal gates can be realized by single or twoparticle scatterings on directed graphs incorporating devices that operate the chirality. As a result, we can design a simple quantum architecture without any need for timedependent control. An application of our procedure to quantum random access memory (qRAM) is also discussed. 
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