42 research outputs found
Steady-state quantum chaos in open quantum systems
We introduce the notion of steady-state quantum chaos as a general phenomenon
in open quantum many-body systems. Classifying an isolated or open quantum
system as integrable or chaotic relies in general on the properties of the
equations governing its time evolution. This however may fail in predicting the
actual nature of the quantum dynamics, that can be either regular or chaotic
depending on the initial state. Chaos and integrability in the steady state of
an open quantum system are instead uniquely determined by the spectral
structure of the time evolution generator. To characterize steady-state quantum
chaos we introduce a spectral analysis based on the spectral statistics of
quantum trajectories (SSQT). We test the generality and reliability of the SSQT
criterion on several dissipative systems, further showing that an open system
with chaotic structure can evolve towards either a chaotic or integrable steady
state. We study steady-state chaos in the driven-dissipative Bose-Hubbard
model, a paradigmatic example of out-of-equilibrium bosonic system without
particle number conservation. This system is widely employed as a building
block in state-of-the-art noisy intermediate-scale quantum devices, with
applications in quantum computation and sensing. Finally, our analysis shows
the existence of an emergent dissipative quantum chaos, where the classical and
semi-classical limits display an integrable behaviour. This emergent
dissipative quantum chaos arises from the quantum and classical fluctuations
associated with the dissipation mechanism. Our work establishes a fundamental
understanding of the integrable and chaotic dynamics of open quantum systems
and paves the way for the investigation of dissipative quantum chaos and its
consequences on quantum technologies.Comment: 23 pages, 12 figure
Strong Coupling Cavity QED with Gate-Defined Double Quantum Dots Enabled by a High Impedance Resonator
The strong coupling limit of cavity quantum electrodynamics (QED) implies the
capability of a matter-like quantum system to coherently transform an
individual excitation into a single photon within a resonant structure. This
not only enables essential processes required for quantum information
processing but also allows for fundamental studies of matter-light interaction.
In this work we demonstrate strong coupling between the charge degree of
freedom in a gate-detuned GaAs double quantum dot (DQD) and a frequency-tunable
high impedance resonator realized using an array of superconducting quantum
interference devices (SQUIDs). In the resonant regime, we resolve the vacuum
Rabi mode splitting of size MHz at a resonator linewidth
MHz and a DQD charge qubit dephasing rate of MHz extracted independently from microwave spectroscopy in the dispersive
regime. Our measurements indicate a viable path towards using circuit based
cavity QED for quantum information processing in semiconductor nano-structures
Fully tunable longitudinal spin-photon interactions in Si and Ge quantum dots
Spin qubits in silicon and germanium quantum dots are promising platforms for
quantum computing, but entangling spin qubits over micrometer distances remains
a critical challenge. Current prototypical architectures maximize transversal
interactions between qubits and microwave resonators, where the spin state is
flipped by nearly resonant photons. However, these interactions cause
back-action on the qubit, that yield unavoidable residual qubit-qubit couplings
and significantly affect the gate fidelity. Strikingly, residual couplings
vanish when spin-photon interactions are longitudinal and photons couple to the
phase of the qubit. We show that large longitudinal interactions emerge
naturally in state-of-the-art hole spin qubits. These interactions are fully
tunable and can be parametrically modulated by external oscillating electric
fields. We propose realistic protocols to measure these interactions and to
implement fast and high-fidelity two-qubit entangling gates. These protocols
work also at high temperatures, paving the way towards the implementation of
large-scale quantum processors
Microwave photon-mediated interactions between semiconductor qubits
The realization of a coherent interface between distant charge or spin qubits
in semiconductor quantum dots is an open challenge for quantum information
processing. Here we demonstrate both resonant and non-resonant photon-mediated
coherent interactions between double quantum dot charge qubits separated by
several tens of micrometers. We present clear spectroscopic evidence of the
collective enhancement of the resonant coupling of two qubits. With both qubits
detuned from the resonator we observe exchange coupling between the qubits
mediated by virtual photons. In both instances pronounced bright and dark
states governed by the symmetry of the qubit-field interaction are found. Our
observations are in excellent quantitative agreement with master-equation
simulations. The extracted two-qubit coupling strengths significantly exceed
the linewidths of the combined resonator-qubit system. This indicates that this
approach is viable for creating photon-mediated two-qubit gates in quantum dot
based systems.Comment: 14 pages, 10 figures and 6 table
Controlling Atom-Photon Bound States in an Array of Josephson-Junction Resonators
Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light -matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. Here, we report on the concept and implementation of a novel microwave architecture consisting of an array of compact superconducting resonators in which we have embedded two frequency -tunable artificial atoms. We study the atom-field interaction and access previously unexplored coupling regimes, in both the single-and double-excitation subspace. In addition, we demonstrate coherent interactions between two atom-photon bound states, in both resonant and dispersive regimes, that are suitable for the implementation of SWAP and CZ two-qubit gates. The presented architecture holds promise for quantum simulation with tunable-range interactions and photon transport experiments in the nonlinear regime
Controlling Atom-Photon Bound States in an Array of Josephson-Junction Resonators
Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light -matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. Here, we report on the concept and implementation of a novel microwave architecture consisting of an array of compact superconducting resonators in which we have embedded two frequency -tunable artificial atoms. We study the atom-field interaction and access previously unexplored coupling regimes, in both the single-and double-excitation subspace. In addition, we demonstrate coherent interactions between two atom-photon bound states, in both resonant and dispersive regimes, that are suitable for the implementation of SWAP and CZ two-qubit gates. The presented architecture holds promise for quantum simulation with tunable-range interactions and photon transport experiments in the nonlinear regime
Strong hole-photon coupling in planar Ge: probing the charge degree and Wigner molecule states
Semiconductor quantum dots (QDs) in planar germanium (Ge) heterostructures
have emerged as frontrunners for future hole-based quantum processors. Notably,
the large spin-orbit interaction of holes offers rapid, coherent electrical
control of spin states, which can be further beneficial for interfacing hole
spins to microwave photons in superconducting circuits via coherent
charge-photon coupling. Here, we present strong coupling between a hole charge
qubit, defined in a double quantum dot (DQD) in a planar Ge, and microwave
photons in a high-impedance ()
superconducting quantum interference device (SQUID) array resonator. Our
investigation reveals vacuum-Rabi splittings with coupling strengths up to
, and a cooperativity of ,
dependent on DQD tuning, confirming the strong charge-photon coupling regime
within planar Ge. Furthermore, utilizing the frequency tunability of our
resonator, we explore the quenched energy splitting associated with
strongly-correlated Wigner molecule (WM) states that emerge in Ge QDs. The
observed enhanced coherence of the WM excited state signals the presence of
distinct symmetries within related spin functions, serving as a precursor to
the strong coupling between photons and spin-charge hybrid qubits in planar Ge.
This work paves the way towards coherent quantum connections between remote
hole qubits in planar Ge, required to scale up hole-based quantum processors.Comment: 22 pages, 12 figure
High-kinetic inductance NbN films for high-quality compact superconducting resonators
Niobium nitride (NbN) is a particularly promising material for quantum
technology applications, as entails the degree of reproducibility necessary for
large-scale of superconducting circuits. We demonstrate that resonators based
on NbN thin films present a one-photon internal quality factor above 10
maintaining a high impedance (larger than 2k), with a footprint of
approximately 50x100 m and a self-Kerr nonlinearity of few tenths of
Hz. These quality factors, mostly limited by losses induced by the coupling to
two-level systems, have been maintained for kinetic inductances ranging from
tenths to hundreds of pH/square. We also demonstrate minimal variations in the
performance of the resonators during multiple cooldowns over more than nine
months. Our work proves the versatility of niobium nitride high-kinetic
inductance resonators, opening perspectives towards the fabrication of compact,
high-impedance and high-quality multimode circuits, with sizable interactions.Comment: 12 pages, 8 figure
Strong coupling between a microwave photon and a singlet-triplet qubit
Tremendous progress in few-qubit quantum processing has been achieved lately
using superconducting resonators coupled to gate voltage defined quantum dots.
While the strong coupling regime has been demonstrated recently for odd charge
parity flopping mode spin qubits, first attempts towards coupling a resonator
to even charge parity singlet-triplet spin qubits have resulted only in weak
spin-photon coupling strengths. Here, we integrate a zincblende InAs nanowire
double quantum dot with strong spin-orbit interaction in a magnetic-field
resilient, high-quality resonator. In contrast to conventional strategies, the
quantum confinement is achieved using deterministically grown wurtzite tunnel
barriers without resorting to electrical gating. Our experiments on even charge
parity states and at large magnetic fields, allow us to identify the relevant
spin states and to measure the spin decoherence rates and spin-photon coupling
strengths. Most importantly, at a specific magnetic field, we find an
anti-crossing between the resonator mode in the single photon limit and a
singlet-triplet qubit with an electron spin-photon coupling strength of MHz, reaching the strong coupling regime in which the coherent
coupling exceeds the combined qubit and resonator linewidth.Comment: 10 pages, 7 figure