JP5554627B2 - Semiconductor electron spin operating method and apparatus - Google Patents

Description

  The present invention relates to a semiconductor electron spin manipulation method and apparatus for manipulating spins of electrons generated in a semiconductor.

  It is known that electron spin has an upward state and a downward state. Since this spin behaves as a quantum, it can take an intermediate state that is a combination of an upward state and a downward state (see Non-Patent Document 1). Accordingly, the electron spin satisfies the basic requirement of the qubit, and a computer can be configured with the electron spin as a basic element (see Non-Patent Document 2). Such a computer using electron spin is called an electron spin quantum computer.

  The basic request for a qubit includes that the intermediate state as previously described can be taken, that the state can be freely controlled (rotation operation), and that initialization can be performed. The direction of the electron spin is usually random, and it is necessary to perform an initialization operation to align it upward or downward. For this initialization, experimental results using a semiconductor quantum dot structure have been reported.

  As one of initialization methods, there is a method of providing an electron injection electrode in a quantum dot structure and applying a magnetic field from the outside (see Non-Patent Document 3). In this method, the injected electrons can be initialized and almost 100% can be initialized. However, an electrode is provided on the element and an external magnetic field is essential for the initialization mechanism.

  As another initialization, there is a report that an experiment was performed in a strong magnetic field using a sample in which a quantum dot structure was doped with electrons without using an electrode (see Non-Patent Document 4). In this method, initialization of 90% or more is realized, but it is very difficult to control the electron density to be initialized, and initialization cannot be realized without an external strong magnetic field.

  It is known that when there is a strong magnetic field, the electronic state has different energy depending on the direction of spin. This is called Zeeman separation. In this state, when a rotation operation necessary for the quantum computer is performed, a process of relaxing to a low energy state occurs (see FIG. 18). Since this relaxation is a random process, the qubit may deviate from the intended movement.

  In addition to this Zeeman separation, the external magnetic field has the effect of polarizing those whose atomic nuclear spin is not zero. This is an effect of changing the electron spin state by acting as a magnetic field, and is called an Overhauser effect (see Non-Patent Document 5). The Overhauser effect changes the spin state and it is very difficult to control the effect, leading to unintended movement of the qubit and degrading the performance of the quantum computer.

  Further, the electrode used in the technique of Non-Patent Document 1 has a drawback that the configuration of the sample is complicated. Further, in the doping method used in the technique of Non-Patent Document 2, the electron concentration is determined depending on the sample, and it is impossible to control the concentration after the sample is manufactured.

Shoichiro Koide, “Quantum Mechanics” (revised version), Hanafusa, 1990. Genadi P. Bellman et al., Translated by Kazunori Matsuda, “Introductory Quantum Computer”, Personal Media, 2002. M. Atature, et al., "Quantum-Dot Spin-State Preparation with Near-Unity Fidelity", SCIENCE, vol.312, pp.551-553, 2006. D. Press1, et al., "Complete quantum control of a single quantum dot spin using ultrafast optical pulses", Nature, Vol. 456, pp. 218-221, 2008. S. W. Brown, et al., "Spectrally resolved overhauser shifts in single GaAs / AlxGa12xAs quantum dots", PHYSICAL REVIEW B, vol.54, no.24, pp.R17 339-R17 342, 1996.

  As described above, the above-described technique has a problem that it is not easy to control the direction of spin of electrons and holes with a simple configuration.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to control the spin directions of electrons and holes with a simple configuration.

In the semiconductor electron spin manipulation method according to the present invention, a barrier section is formed in a confinement structure configured from a confinement section configured to confine carriers composed of a semiconductor and a barrier section composed of a material having a larger energy gap than the confinement section. A first step of generating electrons in the confinement portion by irradiating the first light with energy larger than the energy gap of the material to be encapsulated, and energy in the confinement structure that is larger than the energy gap of the semiconductor and smaller than the energy gap of the material constituting the barrier portion And at least a second step of irradiating a circularly polarized second light selected from clockwise and counterclockwise to generate an exciton in the confinement part, and using an exciton generated by the irradiation of the second light. A part of the generated charge-excited spin-relaxed electrons emits circularly polarized light, and the transition electrons are spin. The relaxation time to be summed is longer than the time for generating the charged excitons by irradiation with the second light. In the second step, a part of the charged excitons generated by generating the excitons emit circularly polarized light and transition to electrons. electronic continuously irradiated with the second light until it you initialized state aligned in the direction of one of the spin.

  In the semiconductor electron spin manipulation method, the confinement structure may be any one selected from a quantum dot structure, a quantum well structure, and a quantum wire structure. In addition, the wavelength of the second light may resonate with the wavelength corresponding to the energy of the charged excitons generated in the confinement part. Moreover, the material which comprises a semiconductor and a barrier part is good in the atom which comprises these not having a nuclear spin.

A semiconductor electron spin manipulating apparatus according to the present invention includes a confinement portion for confining carriers composed of a semiconductor, a confinement structure composed of a barrier portion composed of a material having a larger energy gap than the confinement portion, and the confinement structure. The first light irradiating means for generating electrons in the confinement portion by irradiating the first light having an energy larger than the energy gap of the material constituting the barrier portion, and the barrier portion is formed in the confinement structure larger than the energy gap of the semiconductor. in smaller energy than the energy gap of the material, at least a second light irradiating means for generating an exciton confinement portion by irradiating a second circularly polarized light that is selected from among the right-handed and left-handed, the second Some of the spin-relaxed charged excitons generated by excitons generated by light irradiation emit circularly polarized light The relaxation time for spin relaxation of the transitioned electrons is longer than the time for generating charged excitons by irradiation with the second light, and in the second light irradiation means, a part of the charged excitons generated by the generation of excitons is circular. by emitting polarized light that initializes a state where electrons by continuing the irradiation of the second light are aligned in the direction of one of the spin until the transition to the electronic.

  In the semiconductor electron spin manipulation device, the confinement structure may be any one selected from a quantum dot structure, a quantum well structure, and a quantum wire structure. In addition, the wavelength of the second light may resonate with the wavelength corresponding to the energy of the charged excitons generated in the confinement part. Moreover, the 1st light irradiation means and the 2nd light irradiation means should just be comprised from the laser. Moreover, the material which comprises a semiconductor and a barrier part is good in the atom which comprises these not having a nuclear spin.

  As described above, according to the present invention, the confinement structure is irradiated with the first light having an energy larger than the energy gap of the material constituting the barrier portion, and the barrier is larger than the energy gap of the semiconductor constituting the confinement portion. Since the circularly polarized second light selected from the clockwise and counterclockwise directions is irradiated with an energy smaller than the energy gap of the material constituting the part, the spin of electrons and holes can be reduced with a simple configuration. An excellent effect that the direction can be controlled is obtained.

FIG. 1 is a configuration diagram showing a configuration of a semiconductor electron spin manipulation device according to an embodiment of the present invention. FIG. 2 is a band diagram showing an energy band structure of a quantum well structure in which a barrier layer 201 made of AlGaAs, a well layer 202 made of GaAs, and a barrier layer 203 made of AlGaAs are stacked. FIG. 3 is an explanatory diagram showing response characteristics of electrons and holes confined in the well layer to light incident on the well layer. FIG. 4 is an explanatory diagram for explaining generation of excitons. FIG. 5 is an explanatory diagram for explaining generation of charged excitons. FIG. 6 is an explanatory diagram for explaining generation of charged excitons using energy of electrons and charged excitons. FIG. 7 is an explanatory diagram for explaining initialization of electron spin. FIG. 8 is an explanatory diagram for explaining the spin initialization process. FIG. 9 is an explanatory diagram for explaining a semiconductor electron spin manipulation method according to the embodiment of the present invention. FIG. 10 is an explanatory diagram for explaining generation of excitons and charged excitons. FIG. 11A is a characteristic diagram showing a change in the intensity of photoluminescence obtained from the quantum dot structure. FIG. 11B is a characteristic diagram showing a change in the intensity of photoluminescence obtained from the quantum dot structure. FIG. 12 is an explanatory diagram for explaining a spin state of an atomic nucleus. FIG. 13 is a configuration diagram showing the configuration of the semiconductor electron spin manipulation device according to the first embodiment of the present invention. FIG. 14 is an explanatory diagram for explaining the wavelength of light to be irradiated. FIG. 15 is a configuration diagram showing a configuration of another semiconductor electron spin manipulation device according to the first embodiment of the present invention. FIG. 16 is a configuration diagram showing the configuration of the semiconductor electron spin manipulation device according to the second embodiment of the present invention. FIG. 17 is a configuration diagram showing the configuration of the semiconductor electron spin manipulation device according to the third embodiment of the present invention. FIG. 18 is an explanatory diagram for explaining a process of relaxing to a low energy state by Zeeman separation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a configuration of a semiconductor electron spin manipulation device according to an embodiment of the present invention. This semiconductor electron spin manipulation device includes a confinement structure 103 composed of a confinement part 101 for confining carriers composed of a semiconductor and a barrier part 102 composed of a material having a larger energy gap than the confinement part 101.

  In addition, the semiconductor electron spin manipulation device includes a first light irradiation unit 104 that irradiates the confinement structure 103 with light having energy larger than the energy gap of the material that forms the barrier unit 102, and the energy gap of the semiconductor that forms the confinement unit 101. A second light irradiating unit 105 that irradiates the confinement structure 103 with circularly polarized light selected from among clockwise and counterclockwise with an energy that is larger and smaller than the energy gap of the material constituting the barrier unit 102 Prepare.

  The confinement structure 103 may be, for example, a quantum dot structure including a quantum dot as the confinement part 101 and a barrier layer as the barrier part 102. In addition, the confinement structure 103 may be a quantum well structure including a quantum well as the confinement part 101 and a barrier layer as the barrier part 102, for example. The confinement structure 103 may be, for example, a quantum wire structure constituted by a quantum wire as the confinement portion 101 and a barrier layer as the barrier portion 102. For example, the confinement structure 103 may be a quantum dot structure composed of a quantum dot composed of GaAs and a barrier layer composed of AlGaAs, or a quantum well structure composed of a quantum well composed of GaAs and a barrier layer composed of AlGaAs. As is well known, the confinement part only needs to be formed in a size within a range in which the quantum confinement effect appears.

  In the semiconductor electron spin manipulation device according to the present embodiment described above, first, the energy gap of the material constituting the barrier portion 102 is formed in the confinement structure 103 constituted by the confinement portion 101 and the barrier portion 102 by the first light irradiation unit 104. The first light with larger energy is irradiated, and then the second light irradiation unit 105 causes the confinement structure 103 to be larger than the energy gap of the semiconductor constituting the confinement unit 101 and smaller than the energy gap of the material of the barrier unit 102. By irradiating the circularly polarized second light selected from among clockwise and counterclockwise with energy, the spin direction of the carrier is controlled. Electrons are generated in the confinement part 101 of the confinement structure 103 by the irradiation of the first light, and the spin directions of carriers such as the generated electrons and holes are controlled by the second light irradiation by the second light irradiation part 105. it can.

  Hereinafter, the semiconductor electron spin operation in the present embodiment will be described in more detail. Hereinafter, a quantum well structure in which the well layer is made of GaAs and the barrier layer is made of AlGaAs will be described as an example. FIG. 2 is a band diagram showing an energy band structure of a quantum well structure in which a barrier layer 201 made of AlGaAs, a well layer 202 made of GaAs, and a barrier layer 203 made of AlGaAs are stacked.

  When light with energy larger than the energy gap of AlGaAs constituting the barrier layer 201 is irradiated, electrons and holes are generated. However, since GaAs has a smaller band gap than AlGaAs, as shown in FIG. Holes that are confined in the conduction band of the well layer 202 and are hole holes for electrons are confined in the valence band of the well layer 202.

  FIG. 3 is an explanatory diagram showing response characteristics of electrons and holes confined in the well layer to light incident on the well layer. Due to the band structure characteristics of the semiconductor (GaAs), it is possible to generate upward and downward spins depending on the polarization direction of the circularly polarized light incident on the well layer. Here, circularly polarized light is light having a wavelength corresponding to energy larger than the energy gap of GaAs and smaller than the energy gap of AlGaAs.

  For example, as shown in FIG. 3A, when the well layer is irradiated with right-hand circularly polarized light 311 in the state where the upward spin electrons 301 exist in the valence band, this light is absorbed, and FIG. ), An upward spin electron 302 is generated in the conduction band, and a downward spin hole 303 is generated in the valence band.

  On the other hand, as shown in FIG. 3 (c), when the well layer is irradiated with counterclockwise circularly polarized light 312 in the state where the downward spin electrons 304 exist in the valence band, this light is absorbed, and FIG. As shown in d), downward spin electrons 305 are generated in the conduction band, and upward spin holes 306 are generated in the valence band.

  As described above, the downward spin electrons in the valence band do not respond to the clockwise circularly polarized light, and move to the conduction band only when the counterclockwise circularly polarized light is irradiated.

  As described above, when circularly polarized light is incident, electrons are generated in the conduction band of the well layer, and holes are generated in the valence band. Attraction occurs during the period. As shown in FIG. 4, an attractive force 401 is generated between the electrons 211 and the holes 212 generated in the well layer 202, and the electrons 211 and the holes 212 are constrained by the generated attractive force 401 and are called excitons 402. Will come to form.

  The exciton 402 includes electrons 211 and holes 212, and recombines and emits light as a result of the above-described binding. Further, the polarization direction of the light (circularly polarized light) emitted during this recombination is determined by the spin of electrons and holes as shown in FIG. First, excitons formed by upward spin electrons and downward spin holes emit clockwise circularly polarized light by recombination. On the other hand, excitons formed by downward spin electrons and upward spin holes emit counterclockwise circularly polarized light by recombination.

  Next, charged excitons will be described. For example, as shown in FIG. 5A, when a quantum well structure in which electrons 501 of upward spin are confined in the conduction band of the well layer 202 is irradiated with light 511 that is counterclockwise circularly polarized, As shown in FIG. 5B, the downward spin electrons 502 are generated in the conduction band, and the downward spin electrons 503 are generated in the valence band. Holes 504 are generated.

  On the other hand, even when irradiated with clockwise circularly polarized light, since the upward spin electrons 501 already exist in the conduction band, the absorption of light that causes the upward spin electrons of the valence band to transition to the conduction band is not absorbed. Nothing happens. This is due to the fundamental requirement of quantum mechanics that electrons of the same spin cannot exist in the same energy state. FIG. 5B shows a state in which two electrons and one hole exist, but these are bound to each other in the same manner as excitons to form charged excitons. The example shown in FIG. 5B shows a state of negatively charged excitons in which two electrons and one hole are bound.

  In the above description, the band of the quantum well structure (well layer 202) is described as a reference. However, as shown in FIG. 6, it can also be described using the energy of electrons and charged excitons. Two states 601 and 602 shown in the lower side (ground state) of FIGS. 6A and 6B correspond to states in which electrons exist in advance in the conduction band. Further, two charged excitons 603 and 604 having different hole spin directions are shown on the upper side (excited state) of FIGS. 6A and 6B.

  By using FIG. 6, the control of the state of charged excitons generated using the polarization direction of circularly polarized light can be described in the same manner as the above description using FIG. 5. In the description using FIG. 6, for example, as shown in FIG. 6A, when the clockwise circularly polarized light 611 is irradiated, the charged excitons 603 in which the spin of holes is directed downward are generated. When the charged exciton 603 returns to one electron, light (circularly polarized light) is emitted, but the direction of this polarized light is also clockwise. Further, as shown in FIG. 6B, when the counterclockwise circularly polarized light 612 is irradiated, charged excitons 604 in which the spin of holes is upward are generated. Light is also emitted when the charged exciton 604 returns to electrons, but the direction of this polarization is counterclockwise.

  Next, spin initialization will be described. By using the above-described charged excitons, the spin can be initialized as shown below. First, FIG. 7 is an explanatory diagram for explaining the spin initialization itself. Usually, the direction of the spin of electrons is not determined, and as shown in FIG. 7A, the probabilities when the spin is upward and when the spin is downward are both 0.5. This is an initialized state in which the probability of any direction is set to 1, and the spin initialization is to form such a biased state using some method. In the example shown in FIG. 7B, it is initialized to upward spin.

FIG. 8 is an explanatory diagram for explaining the spin initialization process. First, as shown in FIG. 8B, when the counter-spinning circularly polarized excitation light (second light) 813 is incident in the state where the upward spin electron 804 exists, the upward spin electron 804 responds. As a result, charged excitons 803 with positive spin of holes are generated. In this state, some of the charged excitons 803 emit (emits) counterclockwise circularly polarized light 812 and return to the electrons 804. The other part of the charged excitons 803 transition to the charged excitons 801 through the spin relaxation H of the relaxation time τ _High . Note that the electrons 804 returned by the emission of the left-handed circularly polarized light 812 are absorbed by the excitation light 813 and transition to the charged exciton 803 state.

The charged exciton 801, which is transitioned to the charged exciton 803 by irradiation of the excitation light 813 and is generated by the spin relaxation H, emits (emits) a circularly polarized light 811 with a part of the clockwise polarization, and emits downward spin electrons. Transition to 802. Here, if the relaxation time τ _Low of the spin relaxation L is sufficiently slow, the state of the downward spin electrons 802 is maintained. The charged excitons 801 may return to the charged excitons 803 due to the spin relaxation H, and there is a possibility that the circularly polarized light 812 is emitted to return to the electrons 804. However, if the excitation light 813 is incident, the existing electron 804 immediately transitions to the charged exciton 803, and a part of the electron 802 becomes the electron 802 through the spin relaxation H.

Therefore, if the relaxation time τ _Low of the spin relaxation L is sufficiently longer than the time during which the charged excitons 803 are generated by the incident circularly polarized light 813, the state of the electrons 802 gradually increases and the state of the electrons 802 (electrons are reduced). Spin initialization aligned with downward spin) can be realized. In the above description, the direction of the incident circularly polarized light is described as being counterclockwise, but the same applies to the clockwise direction. When clockwise circular polarized light is incident, charged excitons of spins with upward holes are generated, and spin electrons are generated through spin relaxation H, which are initialized electrons. Spins up.

  Here, in order to make the above-described spin initialization ideal, it is desirable to make the energy of the excitation light resonate with the energy of the charged exciton. Initialization is possible even when there is no resonance, but the characteristics are lower than when resonance occurs.

  Next, generation of electrons that are the basis for generating charged excitons will be described.

  First, electrons are generated by irradiating light having an energy larger than the energy gap of the material constituting the barrier portion constituting the confinement structure. For example, in the case of a quantum well layer composed of a barrier layer made of AlGaAs and a quantum well layer made of GaAs, laser light having a wavelength of 532 nm may be irradiated.

  For example, as shown in FIG. 9A, in a quantum well structure in which a quantum well layer 902 made of GaAs is sandwiched between a barrier layer 901 made of AlGaAs and a barrier layer 903, the quantum well layer 902 has a surface (barrier layer). If it exists near the surface of 903, an electric field exists in the band due to the influence of the surface state, and the band is inclined. In this state, when a quantum well structure is irradiated with a laser beam (green laser) 911 having a wavelength of 532 nm, electrons and holes are generated in the barrier layer 903, the barrier layer 901, and the quantum well layer 902, and are affected by the tilted band. As shown in FIG. 9B, each drifts in the opposite direction.

  As described above, some of the electrons and holes generated by the irradiation of the green laser 911 may be bound to the quantum well layer 902 as shown in FIG. In FIG. 9B, electrons 904 and holes 905 surrounded by a dotted line are bound to the quantum well layer 902. Since the electrons 904 and the holes 905 bound in this way are inclined in band, there is a probability of tunneling in opposite directions. For example, as shown in FIG. 9C, one hole 906 bound to the quantum well layer 902 tunnels to the barrier layer 903. The probability of this tunneling depends strongly on the potential barrier height and thickness of the barrier layer 903 (barrier layer 901), and the probability increases as the barrier becomes lower and the thickness becomes thinner.

As shown in FIG. 9B, it is known that the band offset (ΔE _c ) of the conduction band and the band offset (ΔE _v ) of the valence band are different, and a quantum well structure made of GaAs / AlGaAs. Then, ΔE _c : ΔE _v is 7: 3. For this reason, the probability that holes are tunneled more than electrons is increased, and the probability that only electrons remain in the quantum well layer 902 made of GaAs is increased.

  Here, the electron and hole concentrations initially generated by the irradiation of the green laser 911 depend on the intensity of the irradiated green laser 911, and if this intensity is adjusted, only the electrons remain in the quantum well layer 902. It is also possible to do. When only the electrons remain in the quantum well layer 902 and a quantum well structure is irradiated with a laser beam (red laser) 912 having a wavelength of 720 nm as shown in FIG. Electrons and holes are generated only in the well layer 902. The red laser 912 is light having energy larger than the energy gap of GaAs constituting the quantum well layer 902 and smaller than the energy gap of AlGaAs constituting the barrier layer 901 (barrier layer 903). As a result, as shown in FIG. 9E, excitons 907 due to electrons and holes are formed.

  The electrons and holes generated in the quantum well layer 902 by the irradiation with the red laser 912 may tunnel like the electrons and holes generated by the irradiation with the green laser 911. However, in the irradiation with the red laser 912, since the energy immediately after the generation is small, the electrons and holes are strongly confined in the quantum well layer 902, and the probability that both electrons and holes are tunneled is extremely low. Will come to exist.

  Here, since electrons generated by the irradiation of the green laser 911 are also present in the quantum well layer 902, a bound state is formed with the excitons 907 generated by the irradiation of the red laser 912 as described above, and the charge is charged. An exciton 908 is generated. When charged excitons 908 are generated, initialization can be performed as described with reference to FIG. For example, if the polarization of the red laser 912, which is circularly polarized, is counterclockwise, it is possible to increase the number of downward spin electrons.

  In the above description, the quantum well structure is used. However, in order to generate charged excitons, it is important to match the location where electrons are generated with the location where excitons are generated. In the case of the quantum well structure, the size of electrons and excitons is significantly smaller than the spot size of the light (laser) to be irradiated. For this reason, as shown in FIG. 10A, when the quantum well structure 1001 is irradiated with the green laser 1002 and the red laser 1003, electrons and excitons are not always present in the region 1004 where these irradiations overlap. Absent.

  On the other hand, as shown in FIG. 10B, in the case of the quantum dot structure 1011, the quantum dots are irradiated with the green laser 1012 and the red laser 1013. For this reason, electrons and excitons are generated in the region 1014 where these irradiations overlap, and the locations where the electrons and excitons are generated coincide with each other, so that charged excitons can be generated efficiently.

  FIG. 11A and FIG. 11B show the intensity of photoluminescence (PL) observed (measured) when a GaAs / AlGaAs quantum dot structure is irradiated with a green laser with a wavelength of 532 nm and a circularly polarized red laser with a wavelength of 710 nm. It is a characteristic view which shows (Intensity). The quantum dots are rectangular with a layer thickness of 2.8 nm and a 15 nm square in plan view. FIG. 11A shows a result when the red laser is irradiated, and FIG. 11B shows a result when the red laser and the green laser are irradiated. The measured photoluminescence is that emitted from excitons and charged excitons. Also, the solid line shows the result of clockwise circularly polarized red laser irradiation, and the dotted line shows the result of counterclockwise circularly polarized red laser irradiation.

  As shown in FIG. 11A, photoluminescence from excitons can be seen by irradiation with a red laser. On the other hand, as shown in FIG. 11B, when the green laser and the red laser are irradiated, light emission (photoluminescence) from the charged excitons is observed. There is also a difference between the photoluminescence energy of the excitons and the photoluminescence energy of the charged excitons. This reflects that the charged exciton is a state in which one electron is added to the exciton and exists more stably than the exciton.

  In addition, as shown in FIG. 11B, when light emission from the charged excitons is observed, the light emission intensity from the charged excitons is obtained by the clockwise circularly polarized red laser irradiation and the counterclockwise circularly polarized red laser irradiation. There is a big difference. This ratio is about 1: 3, and referring to the description of FIG. 8, it means that the ratio of the charge excitons 801 and 803 to the emission intensity is about 1: 3.

  Since the light emission process is based on the premise that it is possible to shift to a state after light emission, the ratio of the electrons 804 to which the charged excitons 803 move and the electrons 802 to which the charged excitons 801 move is 1: 3. I understand. The existence probability of the electrons 804 and 802 is 1: 1 when only the green laser is irradiated. On the other hand, the existence probability of the electrons 804 and 802 changes to 1: 3 by irradiating the counterclockwise circularly polarized red laser, and it can be seen that spin initialization can be realized.

  By the way, semiconductors include GaAs, InP, Si, and the like, and there are semiconductors in which the spin of each atomic nucleus is not zero. As shown in FIG. 12A, if the spin of the nucleus (nuclear spin 1201) is not 0, the direction of the nuclear spin 1201 is aligned by the initialized electron spin 1202 as shown in FIG. 12B. The magnetic field 1203 is generated. In this state, as described with reference to FIG. 18, the initialized spin may be relaxed.

The value of the nuclear spin of the material (semiconductor) is determined by the atomic number and mass number of the atoms constituting the material, and Ga and As have values of 3/2, In has a value of 9/2, and the like. However, when the atomic number and the mass number are both even, the spin is 0. Here, when the above-described spin initialization is performed in the quantum dot structure in which the confinement layer is composed of Si and the quantum dots are composed of SiO ₂ , the initialization state is longer than the quantum dot structure composed of GaAs / AlGaAs. It has been confirmed that it is retained. When Si is used, the valence band offset is larger than the conduction band, so that the spin of holes is controlled.

  As described above, according to the present embodiment, it is possible to control the spin directions of electrons and holes with a simple configuration without providing a configuration (external magnetic field) or an electrode for applying a magnetic field. .

  Hereinafter, it demonstrates in detail using an Example.

[Example 1]
First, Example 1 will be described. FIG. 13 is a configuration diagram illustrating the configuration of the semiconductor electron spin manipulation device according to the first embodiment. This semiconductor electron spin manipulation device includes a quantum dot structure 1303 including a quantum dot 1301 made of GaAs and a barrier layer 1302 made of Al _0.3 Ga _0.7 As arranged around the quantum dot 1301. The quantum dot 1301 is a rectangular parallelepiped having a layer thickness of 2.8 nm and a planar view of 15 nm square. If the Al composition of AlGaAs constituting the barrier layer 1302 is increased, electrons and excitons can be confined more strongly in the quantum dots 1301, but the quality (crystallinity) of the semiconductor is deteriorated. On the other hand, when the Al composition is lowered, the crystallinity is improved, but the confinement effect of electrons and excitons in the quantum dots 1301 is weakened.

  The semiconductor electron spin manipulation device includes a laser oscillation device (first light irradiation unit) 1311. The laser oscillation device 1311 emits laser light having a wavelength of 532 nm and irradiates the quantum dot structure 1303. For example, the laser oscillation device 1311 emits a laser beam having a wavelength of 532 nm by combining a semiconductor laser that oscillates at a wavelength of 1064 nm with a YVO crystal and generating a 1064 nm double wave by the YVO crystal.

  The semiconductor electron spin manipulation device further includes a light irradiation unit (second light irradiation unit) 1312 having a laser oscillation device 1312a and a polarization adjuster 1312b that controls the polarization of laser light emitted from the laser oscillation device 1312a. . The laser oscillation device 1312a is constituted by a well-known “Ti-Sapphire” laser, and the wavelength of the emitted laser light can be varied within a range of 710 to 900 nm. The polarization adjuster 1312b is formed of a so-called quarter-wave plate, and changes the polarization of the laser light emitted from the laser oscillation device 1312a to circularly polarized light. The laser oscillation device 1312a and the polarization adjuster 1312b constitute a light irradiation unit (second light irradiation unit) 1312 that irradiates circularly polarized light.

  In this embodiment, first, the quantum dots 1301 can generate electrons and holes by irradiating the quantum dot structure 1303 (quantum dots 1301) with laser light emitted from the laser oscillation device 1311. Here, as described above, the holes tunnel the barrier layer 1302, and electrons remain in the quantum dots 1301. In this state, when the laser light from the laser oscillation device 1312a is transmitted through the polarization adjuster 1312b and irradiated to the quantum dots 1301 as circularly polarized light, charged excitons are generated. At this time, by irradiating laser light having, for example, counterclockwise circularly polarized light with the polarization adjuster 1312b, it is possible to generate downward spin electrons in the quantum dots 1301, as described with reference to FIG. In addition, if this state is continued, the direction of spin of electrons in the quantum dots 1301 can be aligned downward (initialization).

  According to the present embodiment, when the wavelength of the laser light emitted from the laser oscillation device 1312a is 728 nm, initialization can be performed such that the ratio of the downward spin electrons to the upward spin electrons is 3: 1. Further, when the wavelength of the laser light emitted from the laser oscillation device 1312a is 730 nm, initialization can be performed so that the ratio of the downward spin electrons to the upward spin electrons is 5: 1. Further, when the wavelength of the laser light emitted from the laser oscillation device 1312a is 731 nm, initialization can be performed so that the ratio of the downward spin electrons to the upward spin electrons is 10: 1. This wavelength of 731 nm is a wavelength that resonates with the energy of the charged excitons generated in the quantum dots 1301 converted to a wavelength. As described above, the laser light (second light) from the laser oscillation device 1312a has a wavelength that resonates with the energy of the charged exciton, whereby initialization can be performed more efficiently.

  The material constituting the quantum dot structure is not limited to InGaAs / GaAs, and InP / GaP can also be used. In addition, when the GaAs / AlGaAs quantum well structure is used, the characteristics are deteriorated as compared with the case of the quantum dot structure described above, but initialization is possible.

  By the way, the wavelength of the circularly polarized laser beam (second light) for controlling the spin of electrons is such that the energy 1401 corresponding to the wavelength is the band gap of the barrier layer (barrier portion) 1302 as shown in FIG. It needs to be larger. The wavelength of the laser light (first light) for generating electrons (and holes) in the quantum dot 1301 is such that the energy 1402 corresponding to this wavelength is smaller than the band gap of the barrier layer 1302 and the quantum dot (confinement). Part) 1301 may be larger than the band gap.

  In the above description, the laser oscillation device 1311 that emits laser light having a wavelength of 532 nm is used as the first light for generating electrons and holes. However, the present invention is not limited to this. For example, as shown in FIG. 15, a part of the laser light emitted from the laser oscillation device 1312a is extracted by using a semi-reflecting mirror 1501, and the extracted laser light is reflected by a reflecting mirror 1502 to generate a double wave generator 1503. The second harmonic wave may be generated by the second harmonic wave generator 1503 and irradiated to the quantum dots 1301 as the first light 1511. The laser light emitted from the laser oscillation device 1312a and transmitted through the semi-reflecting mirror 1501 is transmitted through the polarization adjuster 1312b and applied to the quantum dots 1301 as circularly polarized second light 1512. Even with this configuration, the direction of electron spin can be controlled and initialization can be performed as described above.

[Example 2]
Next, Example 2 will be described. FIG. 16 is a configuration diagram illustrating the configuration of the semiconductor electron spin manipulation device according to the second embodiment. This semiconductor electron spin manipulation device includes a quantum dot structure 1603 including a quantum dot 1601 made of GaAs and a barrier layer 1602 made of AlGaAs arranged around the quantum dot 1601. The quantum dot structure 1603 is formed on the GaAs substrate 1604.

Further, two semiconductor lasers 1611 and 1612 using an AlGaAs layer formed by crystal growth and a quantum dot structure of GaAs quantum dots are provided on a GaAs substrate 1604. A double wave generator 1613 made of a LiNbO ₃ crystal is formed at the laser beam emitting end of the semiconductor laser 1611. The second harmonic generation unit 1613 can perform an operation of generating a second harmonic by current injection. In addition, a polarization adjuster 1614 for circularly polarized light is provided at the laser light emitting end of the semiconductor laser 1612.

  Also in the present embodiment, the operation of the direction of electron spin can be performed as in the first embodiment. First, the quantum dot structure 1603 (quantum dot 1601) is irradiated with laser light emitted from the semiconductor laser 1611 and transmitted through the second harmonic generation unit 1613, thereby generating electrons and holes in the quantum dot 1601. it can. Here, as described above, the holes tunnel the barrier layer 1602, and electrons remain in the quantum dots 1601. In this state, charged excitons are generated when the laser light from the laser oscillation device 1612 is transmitted through the polarization adjuster 1614 and irradiated to the quantum dots 1601 as circularly polarized light. At this time, for example, by applying laser light in the form of counterclockwise circularly polarized light by the polarization adjuster 1614, the quantum dots 1601 can generate downward spin electrons. In addition, if this state continues, the spin direction of electrons in the quantum dots 1601 can be aligned downward (initialized).

  Note that the semiconductor laser 1611 and the semiconductor laser 1612 may be separately manufactured and attached to the GaAs substrate 1604 by a wafer bonding method.

[Example 3]
Next, Example 3 will be described. FIG. 17 is a configuration diagram illustrating the configuration of the semiconductor electron spin manipulation device according to the third embodiment. This semiconductor electron spin manipulation device includes a quantum dot structure 1703 including a quantum dot 1701 made of Si and a barrier layer 1702 made of silicon oxide disposed around the quantum dot 1701. Further, this semiconductor electron spin manipulation device includes a laser oscillation device (first light irradiation unit) 1711 and a light irradiation unit 1712 (second light irradiation unit). The light irradiation unit 1712 includes a laser oscillation device 1712a and a polarization adjuster 1712b that controls the polarization of the laser light emitted from the laser oscillation device 1712a.

  In this embodiment, first, Si constituting the quantum dot 1701 has no atomic spin because it has 14 atoms and 28 masses. Further, O of silicon oxide constituting the barrier layer 1702 has an atomic number of 8 and a mass number of 16, which also has no nuclear spin. For this reason, the laser oscillation device 1711 in this embodiment is a laser having an emission wavelength of 170 nm, and the laser oscillation device 1712a is a fiber laser having an oscillation wavelength of 1064 nm. The laser emitted from the laser oscillation device 1711 is a sixth harmonic of the fiber laser.

  In this embodiment, in the quantum dot 1701 made of silicon, unlike the description using FIG. 9, the band offset of the valence band is larger than the conduction band. For this reason, in this embodiment, initialization is performed so that the directions of hole spins are unified by irradiation of two laser beams. This initialization state is maintained for a longer time than in the case of the quantum dot structure of GaAs / AlGaAs.

  As described above, according to the present invention, electrons can be generated in a semiconductor, the concentration of generated electrons can be controlled, and initialization of electron spins can be performed without using an external magnetic field and electrodes. The direction of electron spin and hole spin can be controlled. This contributes, for example, to improving the performance of quantum computers using electron spin. Further, since it also serves as a means for controlling the direction of electron spin, it is possible to realize a memory using electron spin. Thus, according to the present invention, the ability of information processing and information recording can be dramatically improved.

  It should be noted that the present invention is not limited to the embodiment described above, and that many modifications can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above description, the second light is irradiated in a state where the first light is irradiated. However, the present invention is not limited to this. If the presence of the electrons generated by the first light irradiation is maintained, the first light irradiation is not necessary after the electrons are generated, and the spin direction can be manipulated by the second light irradiation. The confinement structure is not limited to the quantum dot structure and the quantum well structure, and may be a quantum wire structure.

  DESCRIPTION OF SYMBOLS 101 ... Confinement part, 102 ... Barrier part, 103 ... Confinement structure, 104 ... 1st light irradiation part, 105 ... 2nd light irradiation part.

Claims (9)

In a confinement structure composed of a confinement part confining carriers composed of a semiconductor and a barrier part composed of a material having a larger energy gap than the confinement part, an energy larger than the energy gap of the material constituting the barrier part a first step of generating electrons in said containment portion by irradiating a first light,
The confinement structure is irradiated with circularly polarized second light selected from clockwise and counterclockwise with energy larger than the energy gap of the semiconductor and smaller than the energy gap of the material, and excitons are placed on the confinement portion. And at least a second step of generating ,
The relaxation time in which a part of the charged excitons generated by the excitons generated by the irradiation of the second light and spin-relaxed emits circularly polarized light and the transitioned electrons undergo spin relaxation is determined by the irradiation of the second light. Longer than the time that charged excitons generate,
In the second step, the irradiation of the second light is continued until a part of the charged excitons generated by the generation of the excitons emits circularly polarized light and transitions to electrons, and the electrons are in any spin direction. A method for operating a semiconductor electron spin, wherein the method is initialized to a state in which the semiconductor electron spins are aligned . The semiconductor electron spin manipulation method according to claim 1.
The semiconductor electron spin manipulation method, wherein the confinement structure is selected from a quantum dot structure, a quantum well structure, and a quantum wire structure. The semiconductor electron spin manipulation method according to claim 1 or 2,
The wavelength of said 2nd light resonates with the wavelength corresponding to the energy of the charged exciton produced | generated by the confinement part. The semiconductor electron spin operation method characterized by the above-mentioned. In the semiconductor electron spin operation method according to any one of claims 1 to 3,
A semiconductor electron spin manipulation method, wherein the semiconductor and the material do not have a nuclear spin in atoms constituting them. A confinement structure composed of a confinement portion for confining carriers composed of a semiconductor, and a barrier portion composed of a material having a larger energy gap than the confinement portion;
A first light irradiation means for irradiating the confinement structure with a first light having an energy larger than an energy gap of a material constituting the barrier portion to generate electrons in the confinement portion ;
The confinement structure is irradiated with circularly polarized second light selected from clockwise and counterclockwise with energy larger than the energy gap of the semiconductor and smaller than the energy gap of the material, and excitons are placed on the confinement portion. And at least a second light irradiation means for generating ,
The relaxation time in which a part of the charged excitons generated by the excitons generated by the irradiation of the second light and spin-relaxed emits circularly polarized light and the transitioned electrons undergo spin relaxation is determined by the irradiation of the second light. Longer than the time that charged excitons generate,
The second light irradiation means continues irradiation of the second light until a part of the charged excitons generated by the generation of the excitons emits circularly polarized light and transitions to electrons, whereby any one of the electrons is A semiconductor electron spin manipulating device, which is initialized to a state aligned with a spin direction . The semiconductor electron spin manipulation device according to claim 5, wherein
The semiconductor electron spin manipulation device, wherein the confinement structure is selected from a quantum dot structure, a quantum well structure, and a quantum wire structure. The semiconductor electron spin manipulation device according to claim 5 or 6,
The wavelength of said 2nd light resonates with the wavelength corresponding to the energy of the charged exciton produced | generated by the confinement part. The semiconductor electron spin operation apparatus characterized by the above-mentioned. The semiconductor electron spin manipulation device according to any one of claims 5 to 7,
The semiconductor electron spin manipulation device, wherein the first light irradiation means and the second light irradiation means are constituted by a laser. The semiconductor electron spin manipulation device according to any one of claims 5 to 8,
In the semiconductor and the material, a semiconductor electron spin manipulation device is characterized in that atoms constituting them do not have a nuclear spin.