JQI-QuICS-CMTC Seminar

A game is rigid if a near-optimal score guarantees, under the sole assumption of the validity of quantum mechanics, that the players are using an approximately unique quantum strategy. Rigidity has a vital role in quantum cryptography as it permits a strictly classical user to trust behavior in the quantum realm. This property can be traced back as far as 1998 (Mayers and Yao) and has been proved for multiple classes of games.

Trapped atomic ions are an ideal platform for building novel quantum systems from the ground up. The combination of long-lived qubit coherence time and mature laser manipulation techniques compose the building blocks of a quantum computer. We use this toolbox to engineer interacting many-body systems, where the spins are encoded in atomic hyperfine states and entangled via the shared motional quantum bus.

*Snacks and drinks will served at 4 pm*

*Snacks and drinks will be served at 4 pm*

Trapped atomic ions are a leading platform for quantum information networks, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. However, performing both local and remote operations in a single node of a quantum network requires extreme isolation between spectator qubit memories and qubits associated with the photonic interface. We achieve this isolation by cotrapping 171Yb+ and 138Ba+ qubits.

Searching large databases is an important problem with broad applications. The Grover search algorithm provides a powerful method for quantum computers to perform searches with a quadratic speedup in the number of required database queries over classical computers. Here, we report results for a complete three-qubit Grover search algorithm using the scalable quantum computing technology of trapped atomic ions, with better-than-classical performance. The algorithm is performed for all 8 possible single-result oracles and all 28 possible two-result oracles.

We consider the classical complexity of approximately simulating time evolution under spatially local quadratic bosonic Hamiltonians for time t. We obtain upper bounds on the scaling of t with the number of bosons, n, for which simulation is classically efficient. We also obtain a lower bound on the scaling of t with n for which this problem reduces to a general instance of the boson sampling problem and is hence hard, assuming the conjectures of Aaronson and Arkhipov [Proc. 43rd Annu. ACM Symp. Theory Comput. STOC '11].

We present new composite pulse sequences for performing arbitrary rotations in singlet-triplet qubits that are faster than existing sequences.  We consider two sequences for performing a z rotation, one that generalizes the Hadamard-x-Hadamard sequence, and another that generalizes a sequence by Guy Ramon (G. Ramon, Phys. Rev.

In this talk, I will present recent work on the properties of radiation from a one-dimensional electron liquid. Because of the large mismatch between the speed of light and the Fermi velocity, radiation serves as a direct test of spectral weight of the system which is far `off-shell'. In the Luttinger liquid model, excitations of the electron liquid are described by non-interacting bosons and this spectral weight vanishes. Thus, radiation offers a direct test of behavior which is beyond the Luttinger liquid paradigm.

The gapless surface states of three-dimensional topological insulators are a new form of matter, and there is much active research on exotic order on the surface of topological insulators due to electron-electron interactions. In this talk, we investigate electron-electron interactions on the surface of a three-dimensional topological insulator. First, we construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator.