Atomic Physics Seminars This Term

Quantum computing with neutral atoms has progressed rapidly in recent years, combining large system sizes, flexible and dynamic connectivity, and quickly improving gate fidelities. The pioneering work in this field has been implemented using alkali atoms, primarily rubidium and cesium. However, divalent, alkaline-earth-like atoms such as ytterbium offer significant technical advantages. In this talk, I will present our progress on quantum computing using 171-Yb atoms, including high-fidelity imaging, nuclear spin qubits with extremely long coherence times, and two-qubit gates on nuclear spins using Rydberg states [1,2]. I will also discuss several unexpected benefits of alkaline-earth-atoms: an extremely robust and power-efficient local gate addressing scheme [3], and a novel approach to quantum error correction called “erasure conversion”, which has the potential to implement the surface code with a threshold exceeding 4%, using the unique level structure of 171-Yb to convert spontaneous emission events into erasure errors [4].

 

[1] S. Saskin et al, Phys. Rev. Lett. 122, 143002 (2019).
[2] A. P. Burgers et al, PRX Quantum 3, 020326 (2022).
[3] S. Ma, A. P. Burgers, et al, Phys. Rev. X 12, 021028 (2022).
[4] Y. Wu, et al, Nat. Comms. 13, 4657 (2022).

Macroscopic quantum phenomena, such as observed in superfluids and superconductors, have led to promising technological advancements and some of the most important tests of fundamental physics. At present, quantum detection of light is mostly relegated to the microscale, where avalanche photodiodes are very sensitive to distinguishing single-photon events from vacuum but cannot differentiate between larger photon-number events. Beyond this, the ability to perform measurements to resolve photon numbers is highly desirable for a variety of quantum information applications, including computation, sensing and cryptography. True photon-number resolving detectors do exist, but they are currently limited to the ability to resolve on the order of 10 photons, which is too small for several quantum-state generation methods based on heralded detection. In this talk I’ll explain how we extended photon measurement into the mesoscopic regime by implementing a detection scheme based on multiplexing highly quantum-efficient transition-edge sensors to accurately resolve photon numbers between 0 and 100. Then I’ll demonstrate the use of our system by explaining how we implemented a quantum random-number generator with no inherent bias. This method is based on sampling a coherent state in the photon-number basis and is robust against environmental noise, phase and amplitude fluctuations in the laser, loss and detector inefficiency as well as eavesdropping. Beyond true random-number generation, our detection scheme serves as a means to implement quantum measurement and engineering techniques valuable for photonic quantum information processing.