47 research outputs found
Connecting strongly correlated superfluids by a quantum point contact
Point contacts provide simple connections between macroscopic particle
reservoirs. In electric circuits, strong links between metals, semiconductors
or superconductors have applications for fundamental condensed-matter physics
as well as quantum information processing. However for complex, strongly
correlated materials, links have been largely restricted to weak tunnel
junctions. Here we study resonantly interacting Fermi gases connected by a
tunable, ballistic quantum point contact, finding a non-linear current-bias
relation. At low temperature, our observations agree quantitatively with a
theoretical model in which the current originates from multiple Andreev
reflections. In a wide contact geometry, the competition between superfluidity
and thermally activated transport leads to a conductance minimum. Our system
offers a controllable platform for the study of mesoscopic devices based on
strongly interacting matter.Comment: 5 pages, 4 figures, 7 pages supplementar
A scanning gate microscope for cold atomic gases
We present a scanning probe microscopy technique for spatially resolving
transport in cold atomic gases, in close analogy with scanning gate microscopy
in semiconductor physics. The conductance of a quantum point contact connected
to two atomic reservoirs is measured in the presence of a tightly focused laser
beam acting as a local perturbation that can be precisely positioned in space.
By scanning its position and recording the subsequent variations of
conductance, we retrieve a high-resolution map of transport through a quantum
point contact. We demonstrate a spatial resolution comparable to the extent of
the transverse wave function of the atoms inside the channel, and a position
sensitivity below 10nm. Our measurements agree well with an analytical model
and ab-initio numerical simulations, allowing us to identify a regime in
transport where tunneling dominates over thermal effects. Our technique opens
new perspectives for the high-resolution observation and manipulation of cold
atomic gases.Comment: 5 + 6 pages, 4 + 5 figure
Connecting strongly correlated superfluids by a quantum point contact
Point contacts provide simple connections between macroscopic particle
reservoirs. In electric circuits, strong links between metals, semiconductors
or superconductors have applications for fundamental condensed-matter physics
as well as quantum information processing. However for complex, strongly
correlated materials, links have been largely restricted to weak tunnel
junctions. Here we study resonantly interacting Fermi gases connected by a
tunable, ballistic quantum point contact, finding a non-linear current-bias
relation. At low temperature, our observations agree quantitatively with a
theoretical model in which the current originates from multiple Andreev
reflections. In a wide contact geometry, the competition between superfluidity
and thermally activated transport leads to a conductance minimum. Our system
offers a controllable platform for the study of mesoscopic devices based on
strongly interacting matter.Comment: 5 pages, 4 figures, 7 pages supplementar
Entanglement Stabilization using Parity Detection and Real-Time Feedback in Superconducting Circuits
Fault tolerant quantum computing relies on the ability to detect and correct
errors, which in quantum error correction codes is typically achieved by
projectively measuring multi-qubit parity operators and by conditioning
operations on the observed error syndromes. Here, we experimentally demonstrate
the use of an ancillary qubit to repeatedly measure the and parity
operators of two data qubits and to thereby project their joint state into the
respective parity subspaces. By applying feedback operations conditioned on the
outcomes of individual parity measurements, we demonstrate the real-time
stabilization of a Bell state with a fidelity of in up to 12
cycles of the feedback loop. We also perform the protocol using Pauli frame
updating and, in contrast to the case of real-time stabilization, observe a
steady decrease in fidelity from cycle to cycle. The ability to stabilize
parity over multiple feedback rounds with no reduction in fidelity provides
strong evidence for the feasibility of executing stabilizer codes on timescales
much longer than the intrinsic coherence times of the constituent qubits.Comment: 12 pages, 10 figures. Update: Fig. 5 correcte
Two-terminal transport measurements with cold atoms
In recent years, the ability of cold atom experiments to explore condensed-matter-related questions has dramatically progressed. Transport experiments, in particular, have expanded to the point in which conductance and other transport coefficients can now be measured in a way that is directly analogous to solid-state physics, extending cold-atom-based quantum simulations into the domain of quantum electronic devices. In this topical review, we describe the transport experiments performed with cold gases in the two-terminal configuration, with an emphasis on the specific features of cold atomic gases compared to solid-state physics. We present the experimental techniques and the main experimental findings, focusing on-but not restricted to-the recent experiments performed by our group. We finally discuss the perspectives opened up by this approach, the main technical and conceptual challenges for future developments, and potential applications in quantum simulation for transport phenomena and mesoscopic physics problems