Coherent creation and destruction of orbital wavepackets in Si -P with electrical and optical read-out

At a Glance

Metadata	Details
Publication Date	2015-03-20
Journal	Nature Communications
Authors	K. L. Litvinenko, E. T. Bowyer, P. T. Greenland, N. Stavrias, Juerong Li
Institutions	Radboud University Nijmegen, FELIX Laboratory
Citations	37
Analysis	Full AI Review Included

Technical Analysis and Documentation: Coherent Quantum Control

This documentation analyzes the research paper “Coherent creation and destruction of orbital wavepackets in Si:P with electrical and optical read-out” (Litvinenko et al., 2015) and outlines how 6CCVD’s specialized MPCVD diamond materials and fabrication services can support and advance similar solid-state quantum technology research.

Executive Summary

The research successfully demonstrates coherent control over orbital quantum states in silicon (Si:P) using pulsed Terahertz (THz) radiation and electrical read-out, a crucial step for solid-state quantum computing.

Core Achievement: Coherent creation and destruction of orbital wavepackets (1s $\leftrightarrow$ 2p+) in Si:P via Ramsey interference.
Methodology: Utilized tuneable, transform-limited THz pulses (9.46 THz) from a Free-Electron Laser (FELIX) for excitation.
Read-out: Demonstrated electrical detection of Ramsey fringes using Photothermal Ionization Spectroscopy (PTIS), verified by all-optical photon echo detection.
Quantum Control: Achieved high-precision control, demonstrating milliradian accuracy over the wavefunction phase.
Coherence Metrics: Measured inhomogeneous decoherence time ($T_{2}^{*}$) of 59 $\pm$ 10 ps and spin-lattice relaxation time ($T_{1}$) of 180 ps.
Relevance: Opens a pathway for exploiting donor impurities in silicon for quantum computing schemes that rely on orbital superpositions to gate magnetic exchange interactions.
6CCVD Value: While Si:P is used here, 6CCVD provides the high-purity Single Crystal Diamond (SCD) and Boron-Doped Diamond (BDD) substrates necessary to extend this advanced THz manipulation and quantum control to diamond-based quantum defects (e.g., NV centers), which offer significantly longer coherence times.

Technical Specifications

The following hard data points were extracted from the experimental results, focusing on the physical parameters and measured coherence times.

Parameter	Value	Unit	Context
Excitation Frequency ($f$)	9.46	THz	Resonant with 1s(A₁) $\rightarrow$ 2p+ transition in Si:P
Laser Spectral Width ($\Delta f_{L}$)	0.066 $\pm$ 0.001	THz	Measured via autocorrelation
Laser Pulse Duration ($\Delta\tau_{L}$)	5.7	ps	Minimum pulse duration used
Peak Pulse Fluence ($F$)	0.15	µJ cm^-2	Required for $\pi$/4 pulse area (radius 1 mm)
Inhomogeneous Decoherence Time ($T_{2}^{*}$)	59 $\pm$ 10	ps	Electrically detected Ramsey fringe duration ($\Delta\tau_{R}$)
Spin-Lattice Relaxation Time ($T_{1}$)	180	ps	Determined via photon echo detection
Si:P Donor Concentration	2 $\times$ 10¹⁴	cm^-3	Used for electrical read-out experiment
Electrical Bias Voltage	12	V	Applied across inner contacts for PTIS
Operating Temperature	10	K	Continuous flow cryostat
Wavefunction Phase Control	< 10	nm	Required piezoelectric resolution for mrad control

Key Methodologies

The experiment relied on precise THz pulse generation and sensitive detection techniques to observe quantum coherence in the Si:P system.

THz Excitation Source: A Free-Electron Laser (FELIX) was used to generate coherent, tuneable, pulsed THz radiation, essential for matching the low Rydberg energy of the Si:P donor orbitals.
Pulse Sequence: The core experiment utilized a Ramsey sequence, consisting of two equal-area $\pi$/4 pump pulses (Pulse 1 and Pulse 2) separated by a variable delay ($\tau_{12}$).
Electrical Read-out (PTIS): The sample conductivity was measured as a function of $\tau_{12}$. The detection mechanism, Photothermal Ionization Spectroscopy (PTIS), exploits the much higher thermal ionization probability of the excited 2p state compared to the 1s ground state.
Sample Configuration: Float zone Si:P wafers were used, contacted with four aluminum contacts in a linear arrangement for four-terminal characterization, and maintained at 10 K.
Optical Verification (Photon Echo): An all-optical echo detection scheme was implemented using a three-pulse sequence ($\pi$/4, $\tau_{12}$, $\pi$/4, $\tau_{23}$, $\pi$) to verify coherence independent of inelastic scattering, providing a reliable measure of $T_{1}$ and $T_{2}^{*}$.
Data Processing: Fourier Transform (FT) filtering was applied to the raw time-domain signals to isolate the interference fringes and extract the envelope amplitude, allowing for the determination of $T_{2}^{*}$.

6CCVD Solutions & Capabilities

The demonstrated coherent control techniques are directly transferable to diamond-based quantum systems, which are favored for their superior environmental isolation and coherence properties. 6CCVD is uniquely positioned to supply the necessary advanced diamond materials and fabrication services to replicate or extend this research into the diamond platform.

Research Requirement	6CCVD Applicable Materials & Services	Technical Value Proposition
High-Coherence Quantum Host	Optical Grade Single Crystal Diamond (SCD)	SCD is the ideal platform for solid-state qubits (e.g., NV, SiV centers), offering $T_{2}$ times orders of magnitude longer than Si:P, crucial for scalable quantum computing architectures.
THz/High-Frequency Gating	Boron-Doped Diamond (BDD) Films	BDD provides tunable conductivity and low dielectric loss, enabling the fabrication of integrated THz waveguides, microstrip lines, and high-speed electrical gates necessary for coherent manipulation of quantum defects.
Custom Device Integration	Custom Dimensions & Thickness Control	We supply plates/wafers up to 125 mm (PCD) and precise SCD thicknesses (0.1 µm to 500 µm), allowing researchers to optimize material volume for THz interaction and integrate devices onto specific chip architectures.
Electrical Contact & Read-out	In-House Custom Metalization	6CCVD offers internal deposition of standard contact metals (Au, Pt, Pd, Ti, W, Cu). This capability is essential for creating the precise electrical gates and contacts required for electrical read-out mechanisms, similar to the Al contacts used in the Si:P study.
Minimizing Optical Loss	Ultra-Smooth Polishing (Ra < 1 nm)	SCD substrates are polished to an atomic-scale roughness (Ra < 1 nm), minimizing scattering losses critical for both the THz optical excitation and the all-optical echo detection methods used in this research.

Engineering Support

6CCVD recognizes the complexity of developing quantum devices based on THz manipulation. Our in-house PhD engineering team specializes in MPCVD growth optimization and material selection for similar Quantum Control and THz Spectroscopy projects. We offer consultation to assist researchers in transitioning from Si:P to diamond, ensuring optimal material specifications (e.g., nitrogen concentration control for NV centers) and device integration strategies.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/ncomms7549