75 research outputs found
Ising interaction between capacitively-coupled superconducting flux qubits
Here, we propose a scheme to generate a controllable Ising interaction
between superconducting flux qubits. Existing schemes rely on inducting
couplings to realize Ising interactions between flux qubits, and the
interaction strength is controlled by an applied magnetic field On the other
hand, we have found a way to generate an interaction between the flux qubits
via capacitive couplings. This has an advantage in individual addressability,
because we can control the interaction strength by changing an applied voltage
that can be easily localized. This is a crucial step toward the realizing
superconducting flux qubit quantum computation.Comment: 10 pages, 15 figure
Dynamics of an ultra-strongly-coupled system interacting with a driven nonlinear resonator
In the ultra-strong coupling regime of a light-matter system, the ground
state exhibits non-trivial entanglement between the atom and photons. For the
purposes of exploring the measurement and control of this ground state, here we
analyze the dynamics of such an ultra-strongly-coupled system interacting with
a driven nonlinear resonator acting as a measurement apparatus. Interestingly,
although the coupling between the atom and the nonlinear resonator is much
smaller than the typical energy scales of the ultra-strongly-coupled system, we
show that we can generate a strong correlation between the nonlinear resonator
and the light-matter system. A subsequent coarse- grained measurement on the
nonlinear resonator significantly affects the light-matter system, and the
phase of the light changes depending on the measurement results. Also, we
investigate the conditions for when the nonlinear resonator can be entangled
with the ultra-strongly coupled system, which is the mechanism that allows us
to project the ground state of the ultra-strongly coupled system into a
non-energy eigenstate.Comment: 10 pages, 11 figure
Electron paramagnetic resonance spectroscopy using a single artificial atom
Electron paramagnetic resonance (EPR) spectroscopy is an important technology
in physics, chemistry, materials science, and biology. Sensitive detection with
a small sample volume is a key objective in these areas, because it is crucial,
for example, for the readout of a highly packed spin based quantum memory or
the detection of unlabeled metalloproteins in a single cell. In conventional
EPR spectrometers, the energy transfer from the spins to the cavity at a
Purcell enhanced rate plays an essential role and requires the spins to be
resonant with the cavity, however the size of the cavity (limited by the
wavelength) makes it difficult to improve the spatial resolution. Here, we
demonstrate a novel EPR spectrometer using a single artificial atom as a
sensitive detector of spin magnetization. The artificial atom, a
superconducting flux qubit, provides advantages both in terms of its quantum
properties and its much stronger coupling with magnetic fields. We have
achieved a sensitivity of 400 spins/ with a magnetic
sensing volume around (50 femto-liters). This corresponds
to an improvement of two-order of magnitude in the magnetic sensing volume
compared with the best cavity based spectrometers while maintaining a similar
sensitivity as those spectrometers . Our artificial atom is suitable for
scaling down and thus paves the way for measuring single spins on the nanometer
scale
Scalable quantum computation architecture using always-on Ising interactions via quantum feedforward
Here, we propose a way to control the interaction between qubits with
always-on Ising interaction. Unlike the standard method to change the
interaction strength with unitary operations, we fully make use of non-unitary
properties of projective measurements so that we can effectively turn the
interaction on or off via feedforward. Our scheme is useful to generate two- or
three-dimensional cluster states that are universal resources for
fault-tolerant quantum computation with this scheme, and it provides an
alternative way to realize a scalable quantum proComment: 7 pages, 2 figure
Electron Paramagnetic Resonance Spectroscopy of Er:YSiO Using Josephson Bifurcation Amplifier: Observation of Hyperfine and Quadrupole Structures
We performed magnetic field and frequency tunable electron paramagnetic
resonance spectroscopy of an Er doped YSiO crystal by observing
the change in flux induced on a direct current-superconducting quantum
interference device (dc-SQUID) loop of a tunable Josephson bifurcation
amplifer. The observed spectra show multiple transitions which agree well with
the simulated energy levels, taking into account the hyperfine and quadrupole
interactions of Er. The sensing volume is about 0.15 pl, and our
inferred measurement sensitivity (limited by external flux noise) is
approximately electron spins for a 1 s measurement. The
sensitivity value is two orders of magnitude better than similar schemes using
dc-SQUID switching readout.Comment: Main text: 5 pages, 3 figures. Supplementary materials: 4 pages, 4
figure
Electron paramagnetic resonance spectroscopy using a dc-SQUID magnetometer directly coupled to an electron spin ensemble
We demonstrate electron spin polarization detection and electron paramagnetic
resonance (EPR) spectroscopy using a direct current superconducting quantum
interference device (dc-SQUID) magnetometer. Our target electron spin ensemble
is directly glued on the dc-SQUID magnetometer that detects electron spin
polarization induced by a external magnetic field or EPR in micrometer-sized
area. The minimum distinguishable number of polarized spins and sensing volume
of the electron spin polarization detection and the EPR spectroscopy are
estimated to be and (0.1
pl), respectively.Comment: 9 pages, 3 figure
Observation of collective coupling between an engineered ensemble of macroscopic artificial atoms and a superconducting resonator
The hybridization of distinct quantum systems is now seen as an effective way
to engineer the properties of an entire system leading to applications in
quantum metamaterials, quantum simulation, and quantum metrology. One well
known example is superconducting circuits coupled to ensembles of microscopic
natural atoms. In such cases, the properties of the individual atom are
intrinsic, and so are unchangeable. However, current technology allows us to
fabricate large ensembles of macroscopic artificial atoms such as
superconducting flux qubits, where we can really tailor and control the
properties of individual qubits. Here, we demonstrate coherent coupling between
a microwave resonator and several thousand superconducting flux qubits, where
we observe a large dispersive frequency shift in the spectrum of 250 MHz
induced by collective behavior. These results represent the largest number of
coupled superconducting qubits realized so far. Our approach shows that it is
now possible to engineer the properties of the ensemble, opening up the way for
the controlled exploration of the quantum many-body system
Optically detected magnetic resonance of high-density ensemble of NV centers in diamond
Optically detected magnetic resonance (ODMR) is a way to characterize the NV
centers. Recently, a remarkably sharp dip was observed in the ODMR with a
high-density ensemble of NV centers, and this was reproduced by a theoretical
model in [Zhu et al., Nature Communications 5, 3424 (2014)], showing that the
dip is a consequence of the spin-1 properties of the NV centers. Here, we
present much more details of analysis to show how this model can be applied to
investigate the properties of the NV centers. By using our model, we have
reproduced the ODMR with and without applied magnetic fields. Also, we
theoretically investigate how the ODMR is affected by the typical parameters of
the ensemble NV centers such as strain distributions, inhomogeneous magnetic
fields, and homogeneous broadening width. Our model could provide a way to
estimate these parameters from the ODMR, which would be crucial to realize
diamond-based quantum information processing
Towards Realizing a Quantum Memory for a Superconducting Qubit: Storage and Retrieval of quantum states
We have built a hybrid system composed of a superconducting flux qubit (the
processor) and an ensemble of nitrogen-vacancy centers in diamond (the memory)
that can be directly coupled to one another and demonstrated how information
can be transferred from the flux qubit to the memory, stored and subsequently
retrieved. We have established the coherence properties of the memory, and
succeeded in creating an entangled state between the processor and memory,
demonstrating how the entangled state's coherence is preserved. Our results are
a significant step towards using an electron spin ensemble as a quantum memory
for superconducting qubits.Comment: 5 pages, 3 figure
Improving the lifetime of the NV center ensemble coupled with a superconducting flux qubit by applying magnetic fields
One of the promising systems to realize quantum computation is a hybrid
system where a superconducting flux qubit plays a role of a quantum processor
and the NV center ensemble is used as a quantum memory. We have theoretically
and experimentally studied the effect of magnetic fields on this hybrid system,
and found that the lifetime of the vacuum Rabi oscillation is improved by
applying a few mT magnetic field to the NV center ensemble. Here, we construct
a theoretical model to reproduce the vacuum Rabi oscillations with/without
magnetic fields applied to the NV centers, and we determine the reason why
magnetic fields can affect the coherent properties of the NV center ensemble.
From our theoretical analysis, we quantitatively show that the magnetic fields
actually suppress the inhomogeneous broadening from the strain in the NV
centers
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