Empowering high-dimensional quantum computing by traversing the dual bosonic ladder

  1. Long B. Nguyen,
  2. Noah Goss,
  3. Karthik Siva,
  4. Yosep Kim,
  5. Ed Younis,
  6. Bingcheng Qing,
  7. Akel Hashim,
  8. David I. Santiago,
  9. and Irfan Siddiqi
High-dimensional quantum information processing has emerged as a promising avenue to transcend hardware limitations and advance the frontiers of quantum technologies. Harnessing the
untapped potential of the so-called qudits necessitates the development of quantum protocols beyond the established qubit methodologies. Here, we present a robust, hardware-efficient, and extensible approach for operating multidimensional solid-state systems using Raman-assisted two-photon interactions. To demonstrate its efficacy, we construct a set of multi-qubit operations, realize highly entangled multidimensional states including atomic squeezed states and Schrödinger cat states, and implement programmable entanglement distribution along a qudit array. Our work illuminates the quantum electrodynamics of strongly driven multi-qudit systems and provides the experimental foundation for the future development of high-dimensional quantum applications.

Programmable Heisenberg interactions between Floquet qubits

  1. Long B. Nguyen,
  2. Yosep Kim,
  3. Akel Hashim,
  4. Noah Goss,
  5. Brian Marinelli,
  6. Bibek Bhandari,
  7. Debmalya Das,
  8. Ravi K. Naik,
  9. John Mark Kreikebaum,
  10. Andrew N. Jordan,
  11. David I. Santiago,
  12. and Irfan Siddiqi
The fundamental trade-off between robustness and tunability is a central challenge in the pursuit of quantum simulation and fault-tolerant quantum computation. In particular, many emerging
quantum architectures are designed to achieve high coherence at the expense of having fixed spectra and consequently limited types of controllable interactions. Here, by adiabatically transforming fixed-frequency superconducting circuits into modifiable Floquet qubits, we demonstrate an XXZ Heisenberg interaction with fully adjustable anisotropy. This interaction model is on one hand the basis for many-body quantum simulation of spin systems, and on the other hand the primitive for an expressive quantum gate set. To illustrate the robustness and versatility of our Floquet protocol, we tailor the Heisenberg Hamiltonian and implement two-qubit iSWAP, CZ, and SWAP gates with estimated fidelities of 99.32(3)%, 99.72(2)%, and 98.93(5)%, respectively. In addition, we implement a Heisenberg interaction between higher energy levels and employ it to construct a three-qubit CCZ gate with a fidelity of 96.18(5)%. Importantly, the protocol is applicable to various fixed-frequency high-coherence platforms, thereby unlocking a suite of essential interactions for high-performance quantum information processing. From a broader perspective, our work provides compelling avenues for future exploration of quantum electrodynamics and optimal control using the Floquet framework.

High-Fidelity Qutrit Entangling Gates for Superconducting Circuits

  1. Noah Goss,
  2. Alexis Morvan,
  3. Brian Marinelli,
  4. Bradley K. Mitchell,
  5. Long B. Nguyen,
  6. Ravi K. Naik,
  7. Larry Chen,
  8. Christian Jünger,
  9. John Mark Kreikebaum,
  10. David I. Santiago,
  11. Joel J. Wallman,
  12. and Irfan Siddiqi
Ternary quantum information processing in superconducting devices poses a promising alternative to its more popular binary counterpart through larger, more connected computational spaces
and proposed advantages in quantum simulation and error correction. Although generally operated as qubits, transmons have readily addressable higher levels, making them natural candidates for operation as quantum three-level systems (qutrits). Recent works in transmon devices have realized high fidelity single qutrit operation. Nonetheless, effectively engineering a high-fidelity two-qutrit entanglement remains a central challenge for realizing qutrit processing in a transmon device. In this work, we apply the differential AC Stark shift to implement a flexible, microwave-activated, and dynamic cross-Kerr entanglement between two fixed-frequency transmon qutrits, expanding on work performed for the ZZ interaction with transmon qubits. We then use this interaction to engineer efficient, high-fidelity qutrit CZ† and CZ gates, with estimated process fidelities of 97.3(1)% and 95.2(3)% respectively, a significant step forward for operating qutrits on a multi-transmon device.