Scaling of Dynamical Decoupling for Spin Qubits

Abstract

We investigate the scaling of coherence time T(2) with the number of π pulses n(π) in a singlet-triplet spin qubit using Carr-Purcell-Meiboom-Gill (CPMG) and concatenated dynamical decoupling (CDD) pulse sequences. For an even numbers of CPMG pulses, we find a power law T(2) is proportional to (n(π))(γ(e)), with γ(e)=0.72±0.01, essentially independent of the envelope function used to extract T(2). From this surprisingly robust value, a power-law model of the noise spectrum of the environment, S(ω)~ω(-β), yields β=γ(e)/(1-γ(e))=2.6±0.1. Model values for T(2)(n(π)) using β=2.6 for CPMG with both even and odd n(π) up to 32 and CDD orders 3 through 6 compare very well with the experiment.

Suppression of spin-bath dynamics for improved coherence of multi-spin-qubit systems

“…For a Lorentzian bath, in the limit of very short correlation times (τ c T 2 ), the sequence is inefficient and T 2 ∝n 0 (no improvement with number of pulses). In the opposite limit of very long correlation times τ c  T 2 , the scaling is T 2 ∝n 2/3 (refs 29-31; see also recent work on quantum dots 32 ). In the following we apply spectral decomposition to study the spin-bath dynamics and resulting scaling of T 2 with n for NV centres in diamond.…”

Sensitivity, quantum limits, and quantum enhancement of noise spectroscopies

“…Finally, we show sensitivity beyond the atom-and photon-number-optimized global standard quantum limit using squeezed light. , and quantum information processing [12][13][14][15][16]. By the fluctuation-dissipation theorem, the noise spectrum under thermal equilibrium gives the same information as do driven spectroscopies, with the advantage of characterizing the system in its natural, undisturbed state [17].…”

“…Conclusions -We have derived the sensitivity of noise spectroscopies from estimation theory, finding simple expressions for the Fisher information matrix in terms of the spectral model. The result enables rigorous use of noise spectra in cell biology [5,6], molecular biophysics [7,8], geophysics [9], space science [10], and quantum in- formation processing [12][13][14][15][16]. For optically-probed particulate systems that show line-broadening, e.g.…”

“…Noise spectroscopies, in which naturally occurring fluctuations of a system of interest are recorded by a noninvasive probe, have applications in a wide range of disciplines including atomic [1] and solid state physics [2,3], surface science [4], cell biology [5,6], molecular biophysics [7,8], geophysics [9], space science [10], quantum optomecanics [11], and quantum information processing [12][13][14][15][16]. By the fluctuation-dissipation theorem, the noise spectrum under thermal equilibrium gives the same information as do driven spectroscopies, with the advantage of characterizing the system in its natural, undisturbed state [17].…”

Field-effect-induced two-dimensional electron gas utilizing modulation-doped ohmic contacts

“…A high quality two-dimensional electron gas is induced by a field-effect and is tunable over a wide range of density. Device design, fabrication, and low temperature (T= 0.3K) transport data are reported.Nanostructures such as quantum point contacts and quantum dots fabricated on modulation-doped AlGaAs/GaAs heterostructures are widely used to explore nanoscale electron transport and are utilized extensively in spin-based approaches to quantum computing [1][2][3][4][5][6][7][8]. Modulation-doped GaAs/AlGaAs heterostructures possess several desirable attributes including very high mobility of the underlying two-dimensional electron gas (2DEG) and the relative ease of nanostructure fabrication.…”