Fluxon Readout of a Superconducting Qubit

Fedorov, Kirill G.; Shcherbakova, Anastasia; Wolf, Michael; Beckmann, D.; Ustinov, A. V.

doi:10.1103/physrevlett.112.160502

Cited by 64 publications

(50 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Introduction.-The measurement of the quantum state of a system is a prerequisite ingredient in most modern quantum experiments, ranging from fundamental tests of quantum mechanics [1,2] to various quantuminformation-processing tasks [3][4][5]. However, even with the rapid progress in the coherent manipulation and quantum-state tomography of several quantum systems, such as photons [6,7], electron spins [8][9][10], atomic qubits [11], superconducting circuits [12,13], and mechanical resonators [14,15], many quantum systems still remain difficult to access for a direct observation of their state, systems we will refer to as dark. In order to circumvent the requirement of such a direct access, a promising technique is to employ an auxiliary quantum system as a measurement probe, on which measurements as well as coherent manipulations can be performed [16][17][18][19][20][21][22][23].…”

mentioning

confidence: 99%

Pulsed Quantum-State Reconstruction of Dark Systems

et al. 2019

View full text Add to dashboard Cite

We propose a novel strategy to reconstruct the quantum state of dark systems, i.e., degrees of freedom that are not directly accessible for measurement or control. Our scheme relies on the quantum control of a two-level probe that exerts a state-dependent potential on the dark system. Using a sequence of control pulses applied to the probe makes it possible to tailor the information one can obtain and, for example, allows us to reconstruct the density operator of a dark spin as well as the Wigner characteristic function of a harmonic oscillator. Because of the symmetry of the applied pulse sequence, this scheme is robust against slow noise on the probe. The proof-of-principle experiments are readily feasible in solid-state spins and trapped ions.Introduction.-The measurement of the quantum state of a system is a prerequisite ingredient in most modern quantum experiments, ranging from fundamental tests of quantum mechanics [1, 2] to various quantuminformation-processing tasks [3][4][5]. However, even with the rapid progress in the coherent manipulation and quantum-state tomography of several quantum systems, such as photons [6,7], electron spins [8-10], atomic qubits [11], superconducting circuits [12,13], and mechanical resonators [14,15], many quantum systems still remain difficult to access for a direct observation of their state, systems we will refer to as dark. In order to circumvent the requirement of such a direct access, a promising technique is to employ an auxiliary quantum system as a measurement probe, on which measurements as well as coherent manipulations can be performed [16][17][18][19][20][21][22][23]. Interferometry [24] based on such a measurement probe allows us to extract information on a target system [25][26][27][28][29][30]. Nevertheless, it still remains a key challenge to achieve a full quantum-state tomography of dark systems without requiring any direct control.

show abstract

mentioning

confidence: 99%

Pulsed Quantum-State Reconstruction of Dark Systems

et al. 2019

View full text Add to dashboard Cite

show abstract

“…[10][11][12][13][14][15] It appears that the main drawbacks in its operation come from relativistic effects of the fluxon dynamics. In the experiment, 13,14 the authors used single annular JTL coupled to the qubit instead of a couple, measuring deviation of the fluxon rotation frequency. The measurement results show that this deviation does not depend on the measured magnetic field orientation (the current dipole polarity).…”

mentioning

confidence: 99%

Symmetrical Josephson vortex interferometer as an advanced ballistic single-shot detector

Soloviev

Klenov

Bakurskiy

et al. 2014

Applied Physics Letters

View full text Add to dashboard Cite

We consider a ballistic detector formed in an interferometer manner which operational principle relies on Josephson vortex scattering at a measurement potential. We propose an approach to symmetrize the detector scheme and explore arising advantages in the signal-to-noise ratio and in the back-action on a measured object by means of recently presented numerical and analytical methods for modeling of a soliton scattering dynamics in the presence of thermal fluctuations. The obtained characteristics for experimentally relevant parameters reveal practical applicability of the considered schemes including possibility of coupling with standard digital rapid single flux quantum circuits. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4902327] Ballistic detectors are widely used for mesoscopic quantum measurements.1 In these detectors, a measured system controls a transport of particles by creating a scattering potential. The detector scheme can be organized in an interferometer manner. For example, in the ballistic read-out of superconducting flux qubit, the scheme contains two equal Josephson transmission lines (JTLs), one of which is coupled to the qubit, 2 see Fig. 1(a). Fluxons propagating simultaneously along the JTLs serve as particles in this scheme. The fluxon scattering at the current dipole induced by the qubit magnetic field (see Fig. 1(b)) provides measurable time delay between the moments of arrival of the fluxons to the end of the JTLs. This single-shot, non-projective measurements 3,4 can be made nearly non-demolition by matching the measurement frequency with the frequency of coherent qubit oscillations as described in Ref. 2. Such read-out attracts interest in context of quantum computing which underwent rapid development in the last decade. 5-9A number of works were devoted to theoretical and experimental study of the detector.10-15 It appears that the main drawbacks in its operation come from relativistic effects of the fluxon dynamics. In the experiment, 13,14 the authors used single annular JTL coupled to the qubit instead of a couple, measuring deviation of the fluxon rotation frequency. The measurement results show that this deviation does not depend on the measured magnetic field orientation (the current dipole polarity). The qualitative explanation is that the relativistic fluxon characteristic size becomes much smaller than the dipole length due to Lorenz contraction. Therefore, the total contribution of the successive scatterings at the dipole poles to the frequency shift is independent on the order of the poles. Since the fluxon being inside the coupling loop induces circulating current affecting the qubit, the contraction additionally enhance the back-action. While slow fluxon is obviously preferred to gain the time response, 11,12,15 the corresponding bias current, acting as the fluxon driving force, appears to be unreasonable for the experiment. 12,13 In this work, we study two ways to overcome the discussed drawbacks and show that symmetrization of the coupling leads to signi...

show abstract

“…The fluxon motion in this regime is ballistic, i.e., the velocity v is determined by the process of fluxon injection into the array. In the ballistic regime, fluxon propagation can be used for measurements of superconducting qubits [22][23][24][25]. If small energy losses in the dynamics of the common mode are non-negligible, velocity v of the fluxon motion is established by the balance between these losses and the driving force created by the applied bias current [26][27][28].…”

Section: Basic Model Of Nsquid Arraymentioning

confidence: 99%

nSQUID arrays as conveyers of quantum information

Deng

Averin

2014

J. Exp. Theor. Phys.

View full text Add to dashboard Cite

We have considered the quantum dynamics of an array of nSQUIDs -two-junction SQUIDs with negative mutual inductance between their two arms. Effective dual-rail structure of the array creates additional internal degree of freedom for the fluxons in the array, which can be used to encode and transport quantum information. Physically, this degree of freedom is represented by electromagnetic excitations localized on the fluxon. We have calculated the spatial profile and frequency spectrum of these excitations. Their dynamics can be reduced to two quantum states, so that each fluxons moving through the array carries with it a qubit of information. Coherence properties of such a propagating qubits in the nSQUID array are characterized by the dynamic suppression of the lowfrequency decoherence due to the motion-induced spreading of the noise spectral density to a larger frequency interval.

show abstract

Fluxon Readout of a Superconducting Qubit

Cited by 64 publications

References 33 publications

Pulsed Quantum-State Reconstruction of Dark Systems

Pulsed Quantum-State Reconstruction of Dark Systems

Symmetrical Josephson vortex interferometer as an advanced ballistic single-shot detector

nSQUID arrays as conveyers of quantum information

Contact Info

Product

Resources

About