RESEARCH NEWS & VIEWS temporary information storage, high-speed manipulation techniques must be developed for controlling the single-spin dynamics, such as have been demonstrated for single spins in diamond10. ■ Michael E. Flatté is in the Optical Science and Technology Center and the Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA. e-mail: [email protected] 1. Miyamachi, T. et al. Nature 503, 242–246 (2013). 2. Heinrich, A. J., Gupta, J. A., Lutz, C. P. & Eigler, D. M. Science 306, 466–469 (2004).
3. Tang, J.-M., Levy, J. & Flatté, M. E. Phys. Rev. Lett. 97, 106803 (2006). 4. Yakunin, A. M. et al. Nature Mater. 6, 512–515 (2007). 5. Myers, R. C. et al. Nature Mater. 7, 203–208 (2008). 6. Jelezko, F., Gaebel, T., Popa, I., Gruber, A. & Wrachtrup, J. Phys. Rev. Lett. 92, 076401 (2004). 7. Bar-Gill, N., Pham, L. M., Jarmola, A., Budker, D. & Walsworth, R. L. Nature Commun. 4, 1743 (2013). 8. Balasubramanian, G. et al. Nature Mater. 8, 383–387 (2009). 9. Dobrovitski, V. V., Fuchs, G. D., Falk, A. L., Santori, C. & Awschalom, D. D. Annu. Rev. Condens. Matter Phys. 4, 23–50 (2013). 10. Fuchs, G. D., Dobrovitski, V. V., Toyli, D. M., Heremans, F. J. & Awschalom, D. D. Science 326, 1520–1522 (2009).
BI O D I VER SI T Y
The ecological deficit The almost complete extinction of small mammals in forest islands within 25 years of the construction of a reservoir that fragmented the habitat provides a striking example of delayed biodiversity loss. ANDREW GONZALEZ
G
lobal rates of extinction are set to peak this century1. But it is often difficult to predict when and where species losses will occur, and this hampers efforts to prevent them. Writing in Science, Gibson et al.2 provide an example of things to come, identifying a combination of habitat fragmentation and the arrival of an invasive species as the cause of the extinction of an entire community of small mammals. The extinction sequence was revealed by repeated surveys of the mammalian fauna inhabiting a set of tropical forest islands in southern Thailand that were isolated in 1986 following inundation of the forest to
create the Chiew Larn reservoir. A mathematical model of the biogeography of these islands allowed the authors to estimate the extinction half-life of the mammal communities to be around 14 years — a striking example of an extinction debt. Extinction debt is the idea that species may continue to be lost long after an initial disturbance3,4. Decades of research suggest that small islands of habitat cannot sustain the rich diversity of species they harboured at the time of isolation. Instead, diversity on habitat islands decays exponentially over time in a process called community relaxation5. The number of species lost from the start to the end of the relaxation process is the
12
Number of species
presence of the neighbouring atoms, and also cannot directly occur through an interaction with a passing electron’s spin — the Ho atom spin is oblivious to those interactions. The transition remains possible with two spin-flips with passing electrons, but this requires the Ho spin to be in an intermediate orientation between the two spin-flips, and being in such an orientation costs a lot of energy. For Ho on Pt(111), the most important intermediate orientation is about 8 milli electronvolts (or, equivalently, 100 kelvin) above the ground state (Fig. 1). Thus, if the temperature is much less than 100 K, the twospin-flip transition is extremely unlikely. As a result, at a temperature of 1.1 K, Miyamachi and colleagues measured a spin lifetime that exceeded 6 minutes — a remarkably long value for any solid-state spin system. How does the lifetime of the Ho electronic spin compare with that of single spins in semiconductors? Can a similar energy-level structure be obtained, with the spin-flip of a passing electron unable to cause a transition between the two degenerate lowest-energy states? This configuration occurs for a manganese atom doped into gallium arsenide. In the bulk of gallium arsenide, a manganese atom has a three-fold (angular momentum 1) degenerate ground state, but the application of an electric field3 or a strain field4 can push one state much higher in energy, producing a spin-state level structure that should have long coherence times. Spin coherence times for manganese in gallium arsenide, however, do not exceed 10 nanoseconds5 because of interactions with nuclear spins. Another interesting comparison is with an electronic spin system called the nitrogen vacancy (NV−) centre in diamond6, in which a nitrogen atom and a vacancy replace two neighbouring carbons. That spin centre also has three-fold symmetry, and has two degenerate states. Therefore, the fundamental energy-level structure looks similar to that of Ho on Pt(111). The degenerate states of the NV− centre, however, are not ground states; the ground state is a single state and is split in energy from the other two states by only 5.6 microelectronvolts (Fig. 1).Thus, to keep long spin coherence times (a few milliseconds at room temperature7,8), the spin–orbit inter action must be very small. Miyamachi and colleagues’ exceptionally long lifetimes for single spins adsorbed on a metal strongly support the view that new single-spin candidates with improved fundamental properties can still be found, by careful consideration of the geometry and symmetry of the single spin within its environment. For a long-lived single spin, the effective coherence time can also be dramatically enhanced by careful selection and application of pulses of radiation9. To take full advantage of the long spin lifetimes of Ho on Pt(111) for spin-based computation or
Extinction debt
6
1 0
20
40
Years since isolation
Figure 1 | Isolation leads to extinction. Gibson et al.2 document that within 25 years of the creation of islands by the construction of the Chiew Larn reservoir in Thailand, the diversity of native small mammals on the islands had decreased from up to 12 species to just one. On most of the islands, the only remaining small mammal was the invasive species Rattus tiomanicus, which the authors suggest contributed to the extinctions of native species.
2 0 6 | NAT U R E | VO L 5 0 3 | 1 4 NOV E M B E R 2 0 1 3
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH NEWS & VIEWS temporary information storage, high-speed manipulation techniques must be developed for controlling the single-spin dynamics, such as have been demonstrated for single spins in diamond10. ■ Michael E. Flatté is in the Optical Science and Technology Center and the Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA. e-mail: [email protected] 1. Miyamachi, T. et al. Nature 503, 242–246 (2013). 2. Heinrich, A. J., Gupta, J. A., Lutz, C. P. & Eigler, D. M. Science 306, 466–469 (2004).
3. Tang, J.-M., Levy, J. & Flatté, M. E. Phys. Rev. Lett. 97, 106803 (2006). 4. Yakunin, A. M. et al. Nature Mater. 6, 512–515 (2007). 5. Myers, R. C. et al. Nature Mater. 7, 203–208 (2008). 6. Jelezko, F., Gaebel, T., Popa, I., Gruber, A. & Wrachtrup, J. Phys. Rev. Lett. 92, 076401 (2004). 7. Bar-Gill, N., Pham, L. M., Jarmola, A., Budker, D. & Walsworth, R. L. Nature Commun. 4, 1743 (2013). 8. Balasubramanian, G. et al. Nature Mater. 8, 383–387 (2009). 9. Dobrovitski, V. V., Fuchs, G. D., Falk, A. L., Santori, C. & Awschalom, D. D. Annu. Rev. Condens. Matter Phys. 4, 23–50 (2013). 10. Fuchs, G. D., Dobrovitski, V. V., Toyli, D. M., Heremans, F. J. & Awschalom, D. D. Science 326, 1520–1522 (2009).
BI O D I VER SI T Y
The ecological deficit The almost complete extinction of small mammals in forest islands within 25 years of the construction of a reservoir that fragmented the habitat provides a striking example of delayed biodiversity loss. ANDREW GONZALEZ
G
lobal rates of extinction are set to peak this century1. But it is often difficult to predict when and where species losses will occur, and this hampers efforts to prevent them. Writing in Science, Gibson et al.2 provide an example of things to come, identifying a combination of habitat fragmentation and the arrival of an invasive species as the cause of the extinction of an entire community of small mammals. The extinction sequence was revealed by repeated surveys of the mammalian fauna inhabiting a set of tropical forest islands in southern Thailand that were isolated in 1986 following inundation of the forest to
create the Chiew Larn reservoir. A mathematical model of the biogeography of these islands allowed the authors to estimate the extinction half-life of the mammal communities to be around 14 years — a striking example of an extinction debt. Extinction debt is the idea that species may continue to be lost long after an initial disturbance3,4. Decades of research suggest that small islands of habitat cannot sustain the rich diversity of species they harboured at the time of isolation. Instead, diversity on habitat islands decays exponentially over time in a process called community relaxation5. The number of species lost from the start to the end of the relaxation process is the
12
Number of species
presence of the neighbouring atoms, and also cannot directly occur through an interaction with a passing electron’s spin — the Ho atom spin is oblivious to those interactions. The transition remains possible with two spin-flips with passing electrons, but this requires the Ho spin to be in an intermediate orientation between the two spin-flips, and being in such an orientation costs a lot of energy. For Ho on Pt(111), the most important intermediate orientation is about 8 milli electronvolts (or, equivalently, 100 kelvin) above the ground state (Fig. 1). Thus, if the temperature is much less than 100 K, the twospin-flip transition is extremely unlikely. As a result, at a temperature of 1.1 K, Miyamachi and colleagues measured a spin lifetime that exceeded 6 minutes — a remarkably long value for any solid-state spin system. How does the lifetime of the Ho electronic spin compare with that of single spins in semiconductors? Can a similar energy-level structure be obtained, with the spin-flip of a passing electron unable to cause a transition between the two degenerate lowest-energy states? This configuration occurs for a manganese atom doped into gallium arsenide. In the bulk of gallium arsenide, a manganese atom has a three-fold (angular momentum 1) degenerate ground state, but the application of an electric field3 or a strain field4 can push one state much higher in energy, producing a spin-state level structure that should have long coherence times. Spin coherence times for manganese in gallium arsenide, however, do not exceed 10 nanoseconds5 because of interactions with nuclear spins. Another interesting comparison is with an electronic spin system called the nitrogen vacancy (NV−) centre in diamond6, in which a nitrogen atom and a vacancy replace two neighbouring carbons. That spin centre also has three-fold symmetry, and has two degenerate states. Therefore, the fundamental energy-level structure looks similar to that of Ho on Pt(111). The degenerate states of the NV− centre, however, are not ground states; the ground state is a single state and is split in energy from the other two states by only 5.6 microelectronvolts (Fig. 1).Thus, to keep long spin coherence times (a few milliseconds at room temperature7,8), the spin–orbit inter action must be very small. Miyamachi and colleagues’ exceptionally long lifetimes for single spins adsorbed on a metal strongly support the view that new single-spin candidates with improved fundamental properties can still be found, by careful consideration of the geometry and symmetry of the single spin within its environment. For a long-lived single spin, the effective coherence time can also be dramatically enhanced by careful selection and application of pulses of radiation9. To take full advantage of the long spin lifetimes of Ho on Pt(111) for spin-based computation or
Extinction debt
6
1 0
20
40
Years since isolation
Figure 1 | Isolation leads to extinction. Gibson et al.2 document that within 25 years of the creation of islands by the construction of the Chiew Larn reservoir in Thailand, the diversity of native small mammals on the islands had decreased from up to 12 species to just one. On most of the islands, the only remaining small mammal was the invasive species Rattus tiomanicus, which the authors suggest contributed to the extinctions of native species.
2 0 6 | NAT U R E | VO L 5 0 3 | 1 4 NOV E M B E R 2 0 1 3
© 2013 Macmillan Publishers Limited. All rights reserved
3. Tang, J.-M., Levy, J. & Flatté, M. E. Phys. Rev. Lett. 97, 106803 (2006). 4. Yakunin, A. M. et al. Nature Mater. 6, 512–515 (2007). 5. Myers, R. C. et al. Nature Mater. 7, 203–208 (2008). 6. Jelezko, F., Gaebel, T., Popa, I., Gruber, A. & Wrachtrup, J. Phys. Rev. Lett. 92, 076401 (2004). 7. Bar-Gill, N., Pham, L. M., Jarmola, A., Budker, D. & Walsworth, R. L. Nature Commun. 4, 1743 (2013). 8. Balasubramanian, G. et al. Nature Mater. 8, 383–387 (2009). 9. Dobrovitski, V. V., Fuchs, G. D., Falk, A. L., Santori, C. & Awschalom, D. D. Annu. Rev. Condens. Matter Phys. 4, 23–50 (2013). 10. Fuchs, G. D., Dobrovitski, V. V., Toyli, D. M., Heremans, F. J. & Awschalom, D. D. Science 326, 1520–1522 (2009).
BI O D I VER SI T Y
The ecological deficit The almost complete extinction of small mammals in forest islands within 25 years of the construction of a reservoir that fragmented the habitat provides a striking example of delayed biodiversity loss. ANDREW GONZALEZ
G
lobal rates of extinction are set to peak this century1. But it is often difficult to predict when and where species losses will occur, and this hampers efforts to prevent them. Writing in Science, Gibson et al.2 provide an example of things to come, identifying a combination of habitat fragmentation and the arrival of an invasive species as the cause of the extinction of an entire community of small mammals. The extinction sequence was revealed by repeated surveys of the mammalian fauna inhabiting a set of tropical forest islands in southern Thailand that were isolated in 1986 following inundation of the forest to
create the Chiew Larn reservoir. A mathematical model of the biogeography of these islands allowed the authors to estimate the extinction half-life of the mammal communities to be around 14 years — a striking example of an extinction debt. Extinction debt is the idea that species may continue to be lost long after an initial disturbance3,4. Decades of research suggest that small islands of habitat cannot sustain the rich diversity of species they harboured at the time of isolation. Instead, diversity on habitat islands decays exponentially over time in a process called community relaxation5. The number of species lost from the start to the end of the relaxation process is the
12
Number of species
presence of the neighbouring atoms, and also cannot directly occur through an interaction with a passing electron’s spin — the Ho atom spin is oblivious to those interactions. The transition remains possible with two spin-flips with passing electrons, but this requires the Ho spin to be in an intermediate orientation between the two spin-flips, and being in such an orientation costs a lot of energy. For Ho on Pt(111), the most important intermediate orientation is about 8 milli electronvolts (or, equivalently, 100 kelvin) above the ground state (Fig. 1). Thus, if the temperature is much less than 100 K, the twospin-flip transition is extremely unlikely. As a result, at a temperature of 1.1 K, Miyamachi and colleagues measured a spin lifetime that exceeded 6 minutes — a remarkably long value for any solid-state spin system. How does the lifetime of the Ho electronic spin compare with that of single spins in semiconductors? Can a similar energy-level structure be obtained, with the spin-flip of a passing electron unable to cause a transition between the two degenerate lowest-energy states? This configuration occurs for a manganese atom doped into gallium arsenide. In the bulk of gallium arsenide, a manganese atom has a three-fold (angular momentum 1) degenerate ground state, but the application of an electric field3 or a strain field4 can push one state much higher in energy, producing a spin-state level structure that should have long coherence times. Spin coherence times for manganese in gallium arsenide, however, do not exceed 10 nanoseconds5 because of interactions with nuclear spins. Another interesting comparison is with an electronic spin system called the nitrogen vacancy (NV−) centre in diamond6, in which a nitrogen atom and a vacancy replace two neighbouring carbons. That spin centre also has three-fold symmetry, and has two degenerate states. Therefore, the fundamental energy-level structure looks similar to that of Ho on Pt(111). The degenerate states of the NV− centre, however, are not ground states; the ground state is a single state and is split in energy from the other two states by only 5.6 microelectronvolts (Fig. 1).Thus, to keep long spin coherence times (a few milliseconds at room temperature7,8), the spin–orbit inter action must be very small. Miyamachi and colleagues’ exceptionally long lifetimes for single spins adsorbed on a metal strongly support the view that new single-spin candidates with improved fundamental properties can still be found, by careful consideration of the geometry and symmetry of the single spin within its environment. For a long-lived single spin, the effective coherence time can also be dramatically enhanced by careful selection and application of pulses of radiation9. To take full advantage of the long spin lifetimes of Ho on Pt(111) for spin-based computation or
Extinction debt
6
1 0
20
40
Years since isolation
Figure 1 | Isolation leads to extinction. Gibson et al.2 document that within 25 years of the creation of islands by the construction of the Chiew Larn reservoir in Thailand, the diversity of native small mammals on the islands had decreased from up to 12 species to just one. On most of the islands, the only remaining small mammal was the invasive species Rattus tiomanicus, which the authors suggest contributed to the extinctions of native species.
2 0 6 | NAT U R E | VO L 5 0 3 | 1 4 NOV E M B E R 2 0 1 3
© 2013 Macmillan Publishers Limited. All rights reserved
RESEARCH NEWS & VIEWS temporary information storage, high-speed manipulation techniques must be developed for controlling the single-spin dynamics, such as have been demonstrated for single spins in diamond10. ■ Michael E. Flatté is in the Optical Science and Technology Center and the Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA. e-mail: [email protected] 1. Miyamachi, T. et al. Nature 503, 242–246 (2013). 2. Heinrich, A. J., Gupta, J. A., Lutz, C. P. & Eigler, D. M. Science 306, 466–469 (2004).
3. Tang, J.-M., Levy, J. & Flatté, M. E. Phys. Rev. Lett. 97, 106803 (2006). 4. Yakunin, A. M. et al. Nature Mater. 6, 512–515 (2007). 5. Myers, R. C. et al. Nature Mater. 7, 203–208 (2008). 6. Jelezko, F., Gaebel, T., Popa, I., Gruber, A. & Wrachtrup, J. Phys. Rev. Lett. 92, 076401 (2004). 7. Bar-Gill, N., Pham, L. M., Jarmola, A., Budker, D. & Walsworth, R. L. Nature Commun. 4, 1743 (2013). 8. Balasubramanian, G. et al. Nature Mater. 8, 383–387 (2009). 9. Dobrovitski, V. V., Fuchs, G. D., Falk, A. L., Santori, C. & Awschalom, D. D. Annu. Rev. Condens. Matter Phys. 4, 23–50 (2013). 10. Fuchs, G. D., Dobrovitski, V. V., Toyli, D. M., Heremans, F. J. & Awschalom, D. D. Science 326, 1520–1522 (2009).
BI O D I VER SI T Y
The ecological deficit The almost complete extinction of small mammals in forest islands within 25 years of the construction of a reservoir that fragmented the habitat provides a striking example of delayed biodiversity loss. ANDREW GONZALEZ
G
lobal rates of extinction are set to peak this century1. But it is often difficult to predict when and where species losses will occur, and this hampers efforts to prevent them. Writing in Science, Gibson et al.2 provide an example of things to come, identifying a combination of habitat fragmentation and the arrival of an invasive species as the cause of the extinction of an entire community of small mammals. The extinction sequence was revealed by repeated surveys of the mammalian fauna inhabiting a set of tropical forest islands in southern Thailand that were isolated in 1986 following inundation of the forest to
create the Chiew Larn reservoir. A mathematical model of the biogeography of these islands allowed the authors to estimate the extinction half-life of the mammal communities to be around 14 years — a striking example of an extinction debt. Extinction debt is the idea that species may continue to be lost long after an initial disturbance3,4. Decades of research suggest that small islands of habitat cannot sustain the rich diversity of species they harboured at the time of isolation. Instead, diversity on habitat islands decays exponentially over time in a process called community relaxation5. The number of species lost from the start to the end of the relaxation process is the
12
Number of species
presence of the neighbouring atoms, and also cannot directly occur through an interaction with a passing electron’s spin — the Ho atom spin is oblivious to those interactions. The transition remains possible with two spin-flips with passing electrons, but this requires the Ho spin to be in an intermediate orientation between the two spin-flips, and being in such an orientation costs a lot of energy. For Ho on Pt(111), the most important intermediate orientation is about 8 milli electronvolts (or, equivalently, 100 kelvin) above the ground state (Fig. 1). Thus, if the temperature is much less than 100 K, the twospin-flip transition is extremely unlikely. As a result, at a temperature of 1.1 K, Miyamachi and colleagues measured a spin lifetime that exceeded 6 minutes — a remarkably long value for any solid-state spin system. How does the lifetime of the Ho electronic spin compare with that of single spins in semiconductors? Can a similar energy-level structure be obtained, with the spin-flip of a passing electron unable to cause a transition between the two degenerate lowest-energy states? This configuration occurs for a manganese atom doped into gallium arsenide. In the bulk of gallium arsenide, a manganese atom has a three-fold (angular momentum 1) degenerate ground state, but the application of an electric field3 or a strain field4 can push one state much higher in energy, producing a spin-state level structure that should have long coherence times. Spin coherence times for manganese in gallium arsenide, however, do not exceed 10 nanoseconds5 because of interactions with nuclear spins. Another interesting comparison is with an electronic spin system called the nitrogen vacancy (NV−) centre in diamond6, in which a nitrogen atom and a vacancy replace two neighbouring carbons. That spin centre also has three-fold symmetry, and has two degenerate states. Therefore, the fundamental energy-level structure looks similar to that of Ho on Pt(111). The degenerate states of the NV− centre, however, are not ground states; the ground state is a single state and is split in energy from the other two states by only 5.6 microelectronvolts (Fig. 1).Thus, to keep long spin coherence times (a few milliseconds at room temperature7,8), the spin–orbit inter action must be very small. Miyamachi and colleagues’ exceptionally long lifetimes for single spins adsorbed on a metal strongly support the view that new single-spin candidates with improved fundamental properties can still be found, by careful consideration of the geometry and symmetry of the single spin within its environment. For a long-lived single spin, the effective coherence time can also be dramatically enhanced by careful selection and application of pulses of radiation9. To take full advantage of the long spin lifetimes of Ho on Pt(111) for spin-based computation or
Extinction debt
6
1 0
20
40
Years since isolation
Figure 1 | Isolation leads to extinction. Gibson et al.2 document that within 25 years of the creation of islands by the construction of the Chiew Larn reservoir in Thailand, the diversity of native small mammals on the islands had decreased from up to 12 species to just one. On most of the islands, the only remaining small mammal was the invasive species Rattus tiomanicus, which the authors suggest contributed to the extinctions of native species.
2 0 6 | NAT U R E | VO L 5 0 3 | 1 4 NOV E M B E R 2 0 1 3
© 2013 Macmillan Publishers Limited. All rights reserved
