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Arbitrary photonic wave plate operations on chip: realizing Hadamard, Pauli-X, and rotation gates for polarisation qubits.

Heilmann R, Gräfe M, Nolte S, Szameit A - Sci Rep (2014)

Bottom Line: By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations.Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides.The implemented gates are tested with classical and quantum light.

View Article: PubMed Central - PubMed

Affiliation: Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.

ABSTRACT
Chip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits, and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X, and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light.

No MeSH data available.


Related in: MedlinePlus

Characterisation setups.(a) Classical characterisation of an arbitrary wave plate operation. The relative output of crossed polarisers gives information on the birefringence of the embedded waveguide. (b) Setting for the characterisation of the integrated quantum gates using single photons. One photon of a pair heralds the other one, which is in this case feed to the corresponding quantum gate via a butt-coupled fibre. The HWP 2 determines the measurement basis to be /H〉 and /V〉 or /D〉 and /A〉.
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f4: Characterisation setups.(a) Classical characterisation of an arbitrary wave plate operation. The relative output of crossed polarisers gives information on the birefringence of the embedded waveguide. (b) Setting for the characterisation of the integrated quantum gates using single photons. One photon of a pair heralds the other one, which is in this case feed to the corresponding quantum gate via a butt-coupled fibre. The HWP 2 determines the measurement basis to be /H〉 and /V〉 or /D〉 and /A〉.

Mentions: The birefringent properties of the individual waveguides are obtained by placing a polariser (Pol) at each side of the sample. The polariser after the quarter-wave plate (QWP) is used for preselecting the polarisation direction of the light beam at the input facet. The crossed polariser at the output is then used to analyse the transmitted light. From the positions of the transmission minima as a function of the polariser's rotation angle (see Fig. 4(a)) and the contrast between maxima and minima we are able to deduce the orientation of the optical axis in the waveguide as well as the strength of birefringence. The underlying formula reads as with Itransm/Itotal as relative intensity transmission, αPol as orientation of the first polariser and αwp as optical axis orientation of the evaluated wave plate, Δn as strength of the wave plate's birefringence, k as wave number and z as defect length. It can be seen that the transmitted intensity drops to zero for . Finding those points reveals the orientation of the wave plate's optical axis. In contrast, the maximum intensity transmission always occurs at 45° away from the minimum position. With the used wavelength and the thickness of the wave plate the strength of birefringence can be extracted.


Arbitrary photonic wave plate operations on chip: realizing Hadamard, Pauli-X, and rotation gates for polarisation qubits.

Heilmann R, Gräfe M, Nolte S, Szameit A - Sci Rep (2014)

Characterisation setups.(a) Classical characterisation of an arbitrary wave plate operation. The relative output of crossed polarisers gives information on the birefringence of the embedded waveguide. (b) Setting for the characterisation of the integrated quantum gates using single photons. One photon of a pair heralds the other one, which is in this case feed to the corresponding quantum gate via a butt-coupled fibre. The HWP 2 determines the measurement basis to be /H〉 and /V〉 or /D〉 and /A〉.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3927208&req=5

f4: Characterisation setups.(a) Classical characterisation of an arbitrary wave plate operation. The relative output of crossed polarisers gives information on the birefringence of the embedded waveguide. (b) Setting for the characterisation of the integrated quantum gates using single photons. One photon of a pair heralds the other one, which is in this case feed to the corresponding quantum gate via a butt-coupled fibre. The HWP 2 determines the measurement basis to be /H〉 and /V〉 or /D〉 and /A〉.
Mentions: The birefringent properties of the individual waveguides are obtained by placing a polariser (Pol) at each side of the sample. The polariser after the quarter-wave plate (QWP) is used for preselecting the polarisation direction of the light beam at the input facet. The crossed polariser at the output is then used to analyse the transmitted light. From the positions of the transmission minima as a function of the polariser's rotation angle (see Fig. 4(a)) and the contrast between maxima and minima we are able to deduce the orientation of the optical axis in the waveguide as well as the strength of birefringence. The underlying formula reads as with Itransm/Itotal as relative intensity transmission, αPol as orientation of the first polariser and αwp as optical axis orientation of the evaluated wave plate, Δn as strength of the wave plate's birefringence, k as wave number and z as defect length. It can be seen that the transmitted intensity drops to zero for . Finding those points reveals the orientation of the wave plate's optical axis. In contrast, the maximum intensity transmission always occurs at 45° away from the minimum position. With the used wavelength and the thickness of the wave plate the strength of birefringence can be extracted.

Bottom Line: By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations.Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides.The implemented gates are tested with classical and quantum light.

View Article: PubMed Central - PubMed

Affiliation: Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.

ABSTRACT
Chip-based photonic quantum computing is an emerging technology that promises much speedup over conventional computers at small integration volumes. Particular interest is thereby given to polarisation-encoded photonic qubits, and many protocols have been developed for this encoding. However, arbitrary wave plate operation on chip are not available so far, preventing from the implementation of integrated universal quantum computing algorithms. In our work we close this gap and present Hadamard, Pauli-X, and rotation gates of high fidelity for photonic polarisation qubits on chip by employing a reorientation of the optical axis of birefringent waveguides. The optical axis of the birefringent waveguide is rotated due to the impact of an artificial stress field created by an additional modification close to the waveguide. By adjusting this length of the defect along the waveguide, the retardation between ordinary and extraordinary field components is precisely tunable including half-wave plate and quarter-wave plate operations. Our approach demonstrates the full range control of orientation and strength of the induced birefringence and thus allows arbitrary wave plate operations without affecting the degree of polarisation or introducing additional losses to the waveguides. The implemented gates are tested with classical and quantum light.

No MeSH data available.


Related in: MedlinePlus