Electron spins in semiconductor nanostructures are considered as one of the most promising candidates of the building blocks for quantum information processing. Initialization, coherent manipulation, and measurement of a single electron spin have been recently established. Here we explore the possibility to manipulate and measure by optical means the states of two electrons as a single qubit in nanostructures and propose methods of spin-state tomography based on Faraday or Kerr rotation for cases of both a single electron and two electrons, as well as a method of the Bell-state measurement for two electrons.Electron spins in semiconductor nanostructures are considered as one of the most promising candidates of the building blocks for quantum information processing. Initialization, coherent manipulation, and measurement of a single electron spin have been recently established. Here we explore the possibility to manipulate and measure by optical means the states of two electrons as a single qubit in nanostructures and propose methods of spin-state tomography based on Faraday or Kerr rotation for cases of both a single electron and two electrons, as well as a method of the Bell-state measurement for two electrons.

Journal of the Optical Society of America BMar 16, 20108 citations

Quantum interference of a single spin excitation with a macroscopic atomic ensemble

S. L. Christensen, J.-B. Béguin, Eva Bookjans +4 more

We report on the observation of quantum interference of a collective single spin excitation with a spin ensemble of ${N}_{\mathrm{a}}\ensuremath{\approx}{10}^{5}$ atoms. Detection of a single photon scattered from the atoms creates the single spin excitation, a Fock state embedded in the collective spin of the ensemble. The state of the atomic ensemble is then detected by a quantum nondemolition measurement of the collective spin. A macroscopic difference of the order of ${\sqrt{N}}_{\mathrm{a}}$ in the marginal distribution of the collective spin state arises from the interference between the single excited spin and ${N}_{\mathrm{a}}$ atoms. These hybrid discrete-continuous manipulation and measurement procedures of collective spin states in an atomic ensemble pave the road towards generation of even more exotic ensemble states for quantum information processing, precision measurements, and communication.We report on the observation of quantum interference of a collective single spin excitation with a spin ensemble of ${N}_{\mathrm{a}}\ensuremath{\approx}{10}^{5}$ atoms. Detection of a single photon scattered from the atoms creates the single spin excitation, a Fock state embedded in the collective spin of the ensemble. The state of the atomic ensemble is then detected by a quantum nondemolition measurement of the collective spin. A macroscopic difference of the order of ${\sqrt{N}}_{\mathrm{a}}$ in the marginal distribution of the collective spin state arises from the interference between the single excited spin and ${N}_{\mathrm{a}}$ atoms. These hybrid discrete-continuous manipulation and measurement procedures of collective spin states in an atomic ensemble pave the road towards generation of even more exotic ensemble states for quantum information processing, precision measurements, and communication.

arXiv:1309.2514Physical Review AMar 3, 201430 citations

Detection and Interaction of Single Quantum States

Sishen Xie

Reports of China's Basic ResearchJan 1, 20232 citations

Quantum measurement and feedback with atomic spins

Hideo Mabuchi

APSMay 1, 20040 citations

Coherent spin preparation, manipulation and read-out with light and microwaves in a quantum well and dot

Hideo Kosaka, Hideki Shigyou, Takahiro Inagaki +8 more

Spin is a quantum property of electrons. For spin-based quantum information technology, preparation and read-out of the electron spin state should be spin coherent. We demonstrate that the polarization coher ence of light can be transferred to the spin coherence of electrons in a semiconductor quantum nanostructure [1], and the prepared coherence of the electron spin can also be read out with light by the developed tomographic Kerr rotation method [2]. We also demonstrate that a single photon is efficiently converted (~27%) into a single electron trapped in a gate-defined quantum dot, where the g-factor of electrons is tuned to zero, and the charge state is detected with an adjacent quantum point contact without destructing the spin state [3]. We further demonstrate that the spin coherence of a single electron trapped in one of double quantum dots is electrically manipulated with a microwave applied to the gate and read out via the Pauli spin blockade phenomenon [4]. These demonstrations were carried out in a condition where the up/down spin basis states of electrons remain ed degenerated under an in-plain magnetic field. As this condition ensures the energy conservation between photons and electrons, the entire Poincare sphere representing polarization states of photons can be mapped onto the Bloch sphere representing spin polar ization states of electrons. We theoretically showed that relative spin coherence of two electrons can be also measured with the help of spin-flip tunneling of electrons between the dots [5]. Full Bell state measurement is also possible by the single -spin manipulation and Pauli spin blockade [6]. All of these functions are needed to build all semiconductor quantum repeaters and distributed quantum computers.Spin is a quantum property of electrons. For spin-based quantum information technology, preparation and read-out of the electron spin state should be spin coherent. We demonstrate that the polarization coher ence of light can be transferred to the spin coherence of electrons in a semiconductor quantum nanostructure [1], and the prepared coherence of the electron spin can also be read out with light by the developed tomographic Kerr rotation method [2]. We also demonstrate that a single photon is efficiently converted (~27%) into a single electron trapped in a gate-defined quantum dot, where the g-factor of electrons is tuned to zero, and the charge state is detected with an adjacent quantum point contact without destructing the spin state [3]. We further demonstrate that the spin coherence of a single electron trapped in one of double quantum dots is electrically manipulated with a microwave applied to the gate and read out via the Pauli spin blockade phenomenon [4]. These demonstrations were carried out in a condition where the up/down spin basis states of electrons remain ed degenerated under an in-plain magnetic field. As this condition ensures the energy conservation between photons and electrons, the entire Poincare sphere representing polarization states of photons can be mapped onto the Bloch sphere representing spin polar ization states of electrons. We theoretically showed that relative spin coherence of two electrons can be also measured with the help of spin-flip tunneling of electrons between the dots [5]. Full Bell state measurement is also possible by the single -spin manipulation and Pauli spin blockade [6]. All of these functions are needed to build all semiconductor quantum repeaters and distributed quantum computers.

Journal of Physics Conference SeriesSep 1, 20101 citation

{\sqrt{N}}_{\mathrm{a}}

in the marginal distribution of the collective spin state arises from the interference between the single excited spin and

{N}_{\mathrm{a}}

atoms. These hybrid discrete-continuous manipulation and measurement procedures of collective spin states in an atomic ensemble pave the road towards generation of even more exotic ensemble states for quantum information processing, precision measurements, and communication.