Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G17: Focus Session on Modular, Distributed Quantum Computing: HardwareFocus

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Sponsoring Units: DQI Chair: Liang Jiang, Yale University Room: 203 
Tuesday, March 3, 2020 11:15AM  11:51AM 
G17.00001: RuleSetbased Operation of the Quantum Internet Invited Speaker: Rodney Van Meter The challenges in building a Quantum Internet extend far beyond having a physical layer that can create entanglement across a distance. Quantum Internet nodes must share management of distributed tomography, errors, entanglement swapping, multiplexing of resources, selection of routes, and more to support applicationrequested actions for distributed cryptographic functions, quantum sensor networks, and distributed quantum computation. RuleSetbased operation allows for singlepoint but anylocation decisions on policy for a connection and distributed, realtime selection of actions consistent with those policies. Only such an architecture will provide the full flexibility needed to support intertechnology, interorganizational communications on a longlived, multigenerational Quantum Internet. 
Tuesday, March 3, 2020 11:51AM  12:03PM 
G17.00002: Resourceefficient quantum communication using allphotonic graph states generated from quantum emitters Paul Hilaire, Edwin Barnes, Sophia Economou The emergence of quantum communication technologies shows great promise for applications ranging from the secure transmission of secret messages to distributed quantum computing. Due to fiber losses, longdistance quantum communication requires the use of quantum repeaters, for which there exist quantum memorybased schemes and all photonic schemes. While allphotonic approaches based on graph states generated from linear optics avoid coherence time issues associated with memories, they outperform repeaterless protocols only at the expense of a significant overhead in resources. Here, we consider using quantum emitters to produce the graph states and show how the resource/performance tradeoff can be optimized to yield a protocol that outperforms both repeaterless and memorybased schemes. Our results should pave the way towards the practical implementation of both resourceefficient and fast longdistance quantum communication. 
Tuesday, March 3, 2020 12:03PM  12:15PM 
G17.00003: Stable Polarization Entanglement based Quantum Key Distribution over Metropolitan Fibre network yicheng shi, Moe Thar Soe, Hou Shun Poh, James Anthony Grieve, Christian Kurtsiefer, Alexander Ling We demonstrate a Quantum key distribution (QKD) system implemented with polarisationentangled photons over telecom fibre network. The photon pairs are generated at telecom Oband with one side propagating through 10 km of deployed fibre. Drift of polarisation state over fibre is compensated using liquid crystal variable retarders to minimize the Quantum Bit Error Rate (QBER). This ensures stable, continuous QKD operation with an average QBER of 6.4% and a final key rate of 109 bits/s. 
Tuesday, March 3, 2020 12:15PM  12:27PM 
G17.00004: Experimental Study of an Elementary Cryogenic Microwave Quantum Network Paul Magnard, Philipp Kurpiers, Janis Lütolf, Fabian Marxer, Simon Storz, Josua Schär, Andreas Wallraff Scaling up quantum computers can follow two routes in parallel: increasing the computing power of single processors, and connecting multiple processors into quantum networks using chiptochip deterministic quantum protocols. In both cases, modularity is a key concept. Similarly, the space available at cryogenic temperatures and cooling power needed for superconducting quantum processors can be scaledup in a modular way by connecting dilution refrigerators into cryogenic networks. In this talk, we present an experimental study of essential elements of a cryogenic quantum network. Based on a modular design, we realize a proofofconcept, cryogenic link between two network nodes. We thoroughly analyze the thermal properties of the link elements and extrapolate to distance scales which appear attainable in the presented approach. We also report progress toward transfering quantum information between nodes of the network. 
Tuesday, March 3, 2020 12:27PM  12:39PM 
G17.00005: Rapid transfer of a qubit state into a microwave pulse using a notch Purcell filter Yoshiki Sunada, Shingo Kono, Jesper Ilves, Shuhei Tamate, Yutaka Tabuchi, Yasunobu Nakamura Modules in a distributed quantum computer need to communicate rapidly and coherently with each other. A recent implementation [1] involves transferring the quantum state between a superconducting qubit and an itinerant microwave pulse. To realize highspeed communication with this scheme, the qubit has to be coupled to a waveguide via a lowQ resonator. However, this increases the energy decay rate of the qubit through the Purcell effect. To break this tradeoff, a Purcell filter with a high extinction ratio is required. Here, we use a notch filter to demonstrate the rapid transfer of a qubit state into a microwave pulse. The Purcell decay is suppressed by the destructive interference between multiple decay paths through a multimode resonator. This is realized in a simple device with one port and one coaxial transmission line resonator [2]. We report our progress on analyzing the filter performance and the fidelity of the state transfer. 
Tuesday, March 3, 2020 12:39PM  12:51PM 
G17.00006: A genuine quantum router for microwave photons Zhiling Wang, Zenghui Bao, Yukai Wu, Hongyi Zhang, Yipu Song, Luming Duan A quantum router uses a control qubit to direct the signal qubit to a certain address, which could take a quantum superposition depending on the quantum state of the control qubit. As the elementary building block of a quantum network and a quantum random access memory, the development of a quantum router may accelerate many research fields like quantum entanglement distribution and quantum machine learning. In recent years, many attempts have been made to realize a quantum router in the optical domain. In this talk, I will introduce our experiments of realizing a genuine quantum router in the microwave domain based on superconducting circuit quantum electrodynamics system and demonstrate the coherent routing of a microwave quantum state with high fidelity using a transmon qubit. 
Tuesday, March 3, 2020 12:51PM  1:03PM 
G17.00007: Quantum communication networks with superconducting qubits Youpeng Zhong, Audrey Bienfait, HungShen Chang, MingHan Chou, Christopher R Conner, Etienne Dumur, Joel Grebel, Rhys G Povey, David I Schuster, Andrew Cleland Deterministic state transfer and remote entanglement with microwave photons has recently been demonstrated using different superconducting circuit approaches. More recently, a qubittoqubit transfer fidelity greater than 94% has been achieved in Ref. [1]. This experiment used gmon tunable couplers to control the coupling of the qubits to a 0.78 m long transmission line, achieving few nanosecond tuning speed and large tuning range, thereby allowing for the violation of Bell's inequality in a superconducting quantum communication architecture. In this talk, we examine the scalability of this architecture, and explore more complex quantum communication network designs and protocols. 
Tuesday, March 3, 2020 1:03PM  1:15PM 
G17.00008: Unidirectional emitter and receiver of an itinerant microwave photon in an open waveguide Nicolas Gheeraert, Shingo Kono, Yasunobu Nakamura Quantum networks based on itinerant microwave photons can be an alternative approach toward a largescale superconducting quantum computing. Recently, there have been several implementations of quantum state transfer between two localized superconducting qubits. Toward more complex networking, the control of the propagation direction of itinerant photons, such as routing, switching or circulating, is demanded. Here, we theoretically demonstrate unidirectional emission and absorption of an itinerant microwave photon in an open waveguide using a unit consisting of two superconducting qubits that are parametrically coupled to the waveguide via transfer resonators a quarterwavelength apart. Upon preparing an appropriate entangled state of the two qubits, a photon is then unidirectionally and deterministically emitted to the open waveguide, as a result of the destructive interference — on the right or left of the device — of the radiation emitted from each qubit in both directions. We also show that this twoqubit system is able to deterministically receive a photon arriving from either direction of the waveguide, which cannot be realized with a single qubit. 
Tuesday, March 3, 2020 1:15PM  1:27PM 
G17.00009: Errordetected state transfer and entanglement in a superconducting quantum network: Part 1 James Teoh, Luke Burkhart, Yaxing Zhang, Christopher Axline, Luigi Frunzio, Michel H. Devoret, Liang Jiang, Steven Girvin, Robert Schoelkopf

Tuesday, March 3, 2020 1:27PM  1:39PM 
G17.00010: Errordetected state transfer and entanglement in a superconducting quantum network: Part 2 Luke Burkhart, James Teoh, Yaxing Zhang, Christopher Axline, Luigi Frunzio, Michel H. Devoret, Liang Jiang, Steven Girvin, Robert Schoelkopf We use a quantum bus to transfer qubits and generate entanglement across a twonode network. Crucially, both of these operations can be made less sensitive to loss in the bus by encoding information with multiple photons and detecting loss errors. We transfer a bosonic qubit, tracking loss events to preserve the quantum information, achieving an error rate as low as that in a singlephoton encoding. Further, we generate entanglement with twophoton interference and postselect against errors with local parity measurements, producing a Bell state with a high success probability and half the error of single photon case. These results provide several approaches for highfidelity gates in a quantum network. 
Tuesday, March 3, 2020 1:39PM  1:51PM 
G17.00011: JosephsonPhotonics Devices as a Source of Entangled Microwave Photons Simon Dambach, Ambroise Peugeot, Juha Leppäkangas, Björn Kubala, Marc Westig, Gerbold Ménard, Yuri Mukharsky, Carles Altimiras, Patrice Roche, Philippe Joyez, Denis Vion, Daniel Esteve, Fabien Portier, Joachim Ankerhold The realization and characterization of efficient sources of entangled microwave photons is of paramount importance for many future applications of quantum technology. Josephsonphotonics devices are very promising candidates for this task since they allow one to create a broad range of different entangled states in a surprisingly simple and robust way. These devices consist of a dcvoltage–biased Josephson junction which is placed in series to several microwave cavities. Steady states with multifaceted entanglement properties are reached here naturally due to the interplay of multiphoton creation processes by the Josephson current and subsequent individual photon leakage from the cavities. In this talk, we present a detailed theoretical study of the bipartite entanglement between photon pairs in the output transmission lines. Numerical simulations, taking into account lowfrequency fluctuations of the bias voltage and the finite bandwidth of microwave signal detectors, show excellent agreement with recent experimental data. 
Tuesday, March 3, 2020 1:51PM  2:03PM 
G17.00012: Superconducting Qubits for Robust Remote Entanglement via Adiabatic State Transfer HungShen Chang, Youpeng Zhong, Audrey Bienfait, MingHan Chou, Christopher R Conner, Etienne Dumur, Joel Grebel, Gregory Peairs, Rhys G Povey, Kevin Satzinger, Andrew Cleland Efficient quantum communication between remote quantum nodes relies on high fidelity quantum state transfer and entanglement generation. Loss in the communication channel connecting the quantum nodes can significantly limit the efficiency of these processes. One proposed method to overcome channel loss is to use adiabatic protocols to transfer quantum states without populating the lossy communication channel. Here we construct and operate a superconducting system to test such methods, using two superconducting qubits connected by a 0.73 m long transmission channel, where the channel loss can be externally varied over two orders of magnitude (as measured by the Q of the resonant channel modes). We demonstrate that in the limit of low loss, an adiabatic passage method performs as well as previously demonstrated relay method [1], while in the presence of strong loss, the adiabatic passage achieves states transfer and entanglement fidelities more than a factor of two larger than the relay method. 
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