25 research outputs found
Observation of entanglement negativity transition of pseudo-random mixed states
Multipartite entanglement is a key resource for quantum computation. It is
expected theoretically that entanglement transition may happen for multipartite
random quantum states, however, which is still absent experimentally. Here, we
report the observation of entanglement transition quantified by negativity
using a fully connected 20-qubit superconducting processor. We implement
multi-layer pseudo-random circuits to generate pseudo-random pure states of 7
to 15 qubits. Then, we investigate negativity spectra of reduced density
matrices obtained by quantum state tomography for 6 qubits.Three different
phases can be identified by calculating logarithmic negativities based on the
negativity spectra. We observe the phase transitions by changing the sizes of
environment and subsystems. The randomness of our circuits can be also
characterized by quantifying the distance between the distribution of output
bit-string probabilities and Porter-Thomas distribution. Our simulator provides
a powerful tool to generate random states and understand the entanglement
structure for multipartite quantum systems
On-chip black hole: Hawking radiation and curved spacetime in a superconducting quantum circuit with tunable couplers
Hawking radiation is one of quantum features of a black hole, which can be
understood as a quantum tunneling across the event horizon of the black hole,
but it is quite difficult to directly observe the Hawking radiation of an
astrophysical black hole. Remarkable experiments of analogue black holes on
various platforms have been performed. However, Hawking radiation and its
quantum nature such as entanglement have not been well tested due to the
experimental challenges in accurately constructing curved spacetime and
precisely measuring the thermal spectrum. Based on the recent architecture
breakthrough of tunable couplers for superconducting processor, we realize
experimentally an analogue black hole using our new developed chip with a chain
of 10 superconducting transmon qubits with interactions mediated by 9
transmon-type tunable couplers. By developing efficient techniques to engineer
the couplings between qubits via tuning couplers, we realize both the flat and
curved spacetime backgrounds. The quantum walks of quasi-particle in the curved
spacetime reflect the gravitational effect around the black hole, resulting in
the behavior of Hawking radiation. By virtue of the state tomography
measurement of all 7 qubits outside the analogue event horizon, we show that
Hawking radiation can be verified. In addition, an entangled pair is prepared
inside the horizon and the dynamics of entanglement in the curved spacetime is
directly measured. Our results would stimulate more interests to explore
information paradox, entropy and other related features of black holes using
programmable superconducting processor with tunable couplers.Comment: modified manuscripts, 7 pages, 4 figures (main text) + 12 pages
(supplementary information
Quantum simulation of topological zero modes on a 41-qubit superconducting processor
Quantum simulation of different exotic topological phases of quantum matter
on a noisy intermediate-scale quantum (NISQ) processor is attracting growing
interest. Here, we develop a one-dimensional 43-qubit superconducting quantum
processor, named as Chuang-tzu, to simulate and characterize emergent
topological states. By engineering diagonal
Aubry-Andr-Harper (AAH) models, we experimentally
demonstrate the Hofstadter butterfly energy spectrum. Using Floquet
engineering, we verify the existence of the topological zero modes in the
commensurate off-diagonal AAH models, which have never been experimentally
realized before. Remarkably, the qubit number over 40 in our quantum processor
is large enough to capture the substantial topological features of a quantum
system from its complex band structure, including Dirac points, the energy
gap's closing, the difference between even and odd number of sites, and the
distinction between edge and bulk states. Our results establish a versatile
hybrid quantum simulation approach to exploring quantum topological systems in
the NISQ era.Comment: Main text: 6 pages, 4 figures; Supplementary: 16 pages, 14 figure
Data
The rar file contains the original data of Figure 1 to Figure 6, and Figure S1 to Figure S6
Data from: Facile synthesis of NiCo2S4/CNTs nanocomposites for high-performance supercapacitors
Herein, porous NiCo2S4/CNTs nanocomposites were synthesized via a simple hydrothermal method followed by the sulfurization process using different sulfide sources. By comparing two different sulfur sources, the samples using thioacetamide as sulfide source delivered more remarkable electrochemical performance with a high specific capacitance of 1765 F/g at 1 A/g and an admirable cycling stability with capacitance retention of 71.7% at a high current density of 10 A/g after 5000 cycles in 2 M KOH aqueous electrolyte. Furthermore, an asymmetric supercapacitor (ASC) device was successfully fabricated with the NiCo2S4/CNTs electrode as the positive electrode and graphene as the negative electrode. The device provided a maximum energy density of 29.44 Wh/kg at a power density of 812 W/kg. Even at a high power density of 8006 W/kg, the energy density still reaches 16.68 Wh/kg. Moreover, the ASC presents 89.8% specific capacitance retention after 5000 cycles at 5 A/g. These results reveal its great potential for supercapacitors in electrochemical energy storage field