Quantum Computing Seminars take place on Wednesdays at 3 pm at CSI (Bldg 725) Training Room, unless otherwise noted. All events are free and open to the public. For questions please contact Layla Hormozi.
OCT
23
Wednesday
CSI Q Seminar
"Universal logical gate sets with constant-depth circuits for topological and hyperbolic quantum codes"
Presented by Guanyu Zhu, IBM T.J. Watson Research Center
3 pm, Conference Room 201, Bldg 734
Wednesday, October 23, 2019, 3:00 pm
Hosted by: Layla Hormozi
A fundamental question in the theory of quantum computation is to understand the ultimate space-time resource costs for performing a universal set of logical quantum gates to arbitrary precision. To date, common approaches for implementing a universal logical gate set, such as schemes utilizing magic state distillation, require a substantial space-time overhead. In this work, we show that braids and Dehn twists, which generate the mapping class group of a generic high genus surface and correspond to logical gates on encoded qubits in arbitrary topological codes, can be performed through a constant depth circuit acting on the physical qubits. In particular, the circuit depth is independent of code distance d and system size. The constant depth circuit is composed of a local quantum circuit, which implements a local geometry deformation, and a permutation of qubits. When applied to anyon braiding or Dehn twists in the Fibonacci Turaev-Viro code based on the Levin-Wen model, our results demonstrate that a universal logical gate set can be implemented on encoded qubits in O(1) time through a constant depth unitary quantum circuit, and without increasing the asymptotic scaling of the space overhead. Our results for Dehn twists can be extended to the context of hyperbolic Turaev-Viro codes as well, which have constant space overhead (constant rate encoding). This implies the possibility of achieving a space-time overhead of O(d/log d), which is optimal to date. From a conceptual perspective, our results reveal a deep connection between the geometry of quantum many-body states and the complexity of quantum circuits. References: arXiv:1806.06078,arXiv:1806.02358, Quantum 3, 180 (2019) (arXiv:1901.11029).
OCT
30
Wednesday
CSI Q Seminar
"Characterizing readout in quantum computers: does the reading '0' really mean 0 and '1' really 1?"
Presented by Tzu-Chieh Wei, Stony Brook University
3 pm, Training Room, Bldg 725
Wednesday, October 30, 2019, 3:00 pm
Hosted by: Layla Hormozi
Typical quantum computation includes three stages: state initialization, gate operations and readout. There are tomographic tools on quantum state and process tomography, as well as one that is often ignored, i.e. the detector tomography. It is important to characterize the readout in interpreting experiments on quantum computers. We use quantum detector tomography to characterize the qubit readout in terms of measurement POVMs on IBM Quantum Computers (e.g. IBM Q 5 Tenerife and IBM Q 5 Yorktown). Our results suggest that the characterized detector model deviates from the ideal projectors, ranging from 10 to 40 percent. This is mostly dominated by classical errors, evident from the shrinkage of arrows in the corresponding Bloch-vector representations. There are also small deviations that are not `classical', of order 3 percent or less, represented by the tilt of the arrows from the z axis. Further improvement on this characterization can be made by adopting two- or more-qubit detector models instead of independent single-qubit detectors for all the qubits in one device. We also find evidence indicating correlations in the detector behavior, i.e. the detector characterization is slightly altered (to a few percent) when other qubits and their detectors are in operation. Such peculiar behavior is consistent with characterization from the more sophisticated approach of the gate set tomography. Finally, we also discuss how the characterized detectors' POVM, despite deviation from the ideal projectors, can be used to estimate the ideal detection distribution.
NOV
13
Wednesday
CSI Q Seminar
"Quantum Information: History, Development and Applications"
Presented by Vladimir Korepin, Stony Brook University
3 pm, Training Room, Bldg 725
Wednesday, November 13, 2019, 3:00 pm
Hosted by: Layla Hormozi
History and information theory will be briefly mentioned. Entanglement in spin chains and applications will be reviewed. Algorithms will be mentioned (specifically quantum search).
DEC
18
Wednesday
CSI Q Seminar
"Probing quantum entanglement at the Electron Ion Collider"
Presented by Dmitri Kharzeev, Stony Brook University and BNL
3 pm, Training Room, Bldg 725
Wednesday, December 18, 2019, 3:00 pm
Hosted by: Layla Hormozi
The structure functions measured in deep-inelastic scattering are related to the entropy of entanglement between the region probed by the virtual photon and the rest of the hadron. This opens new possibilities for experimental and theoretical studies using the Electron Ion Collider. The real-time evolution of the final state in deep-inelastic scattering can be addressed with quantum simulations using the duality between high energy QCD and the Heisenberg spin chain.
CSI Q Seminar
"Quantum simulation of quantum field theory on the light front"
Presented by Peter Love, Tufts University and BNL
Tuesday, October 15, 2019, 12 pm
Training Room, Bldg 725
Hosted by: Layla Hormozi
Quantum simulation proposes to use future quantum computers to calculate properties of quantum systems. The simulation of quantum field theories by any means is a challenge, and quantum algorithms for problems in fundamental physics are a natural target for quantum computation. We will show that the light front formulation of quantum field theory is particularly useful in this regard. We analyze a simple theory in 1 + 1D and show how computation of quantities of interest in this theory is analogous to quantum algorithms for chemistry that we understand in detail.