We improve the number of T gates needed to perform an n-bit adder from $8n + O(1)$ to $4n + O(1)$. We do so via a "temporary logical-AND" construction which uses four T gates to store the logical-AND of two qubits into an ancilla and zero T gates to later erase the ancilla. This construction is equivalent to one by Jones, except that our framing makes it clear that the technique is far more widely applicable than previously realized. Temporary logical-ANDs can be applied to integer arithmetic, modular arithmetic, rotation synthesis, the quantum Fourier transform, Shor's algorithm, Grover oracles, and many other circuits. Because T gates dominate the cost of quantum computation based on the surface code, and temporary logical-ANDs are widely applicable, this represents a significant reduction in projected costs of quantum computation. In addition to our n-bit adder, we present an n-bit controlled adder circuit with T-count of $8n + O(1)$, a temporary adder that can be computed for the same cost as the normal adder but whose result can be kept until it is later uncomputed without using T gates, and discuss some other constructions whose T-count is improved by the temporary logical-AND.
 M. Amy, D. Maslov, M. Mosca, and M. Roetteler. A meet-in-the-middle algorithm for fast synthesis of depth-optimal quantum circuits. IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 32 (6): 818-830, jun 2013. 10.1109/tcad.2013.2244643.
 Ryan Babbush, Craig Gidney, Dominic W Berry, Nathan Wiebe, Jarrod McClean, Alexandru Paler, Austin Fowler, and Hartmut Neven. Encoding electronic spectra in quantum circuits with linear T complexity. arXiv preprint arXiv:1805.03662, 2018. URL https://arxiv.org/abs/1805.03662.
 Adriano Barenco, Charles H. Bennett, Richard Cleve, David P. DiVincenzo, Norman Margolus, Peter Shor, Tycho Sleator, John A. Smolin, and Harald Weinfurter. Elementary gates for quantum computation. Physical Review A, 52 (5): 3457-3467, nov 1995. 10.1103/physreva.52.3457.
 R. Barends, J. Kelly, A. Megrant, A. Veitia, D. Sank, E. Jeffrey, T. C. White, J. Mutus, A. G. Fowler, B. Campbell, Y. Chen, Z. Chen, B. Chiaro, A. Dunsworth, C. Neill, P. O'Malley, P. Roushan, A. Vainsencher, J. Wenner, A. N. Korotkov, A. N. Cleland, and John M. Martinis. Superconducting quantum circuits at the surface code threshold for fault tolerance. Nature, 508: 500-503, 2014. 10.1038/nature13171. arXiv:1402.4848.
 S. B. Bravyi and A. Yu. Kitaev. Quantum codes on a lattice with boundary. arXiv:quant-ph/9811052, 1998. URL https://arxiv.org/abs/quant-ph/9811052.
 Steven A. Cuccaro, Thomas G. Draper, Samuel A. Kutin, and David Petrie Moulton. A new quantum ripple-carry addition circuit, 2004. URL https://arxiv.org/abs/quant-ph/0410184.
 E. Dennis, A. Kitaev, A. Landahl, and J. Preskill. Topological quantum memory. J. Math. Phys., 43: 4452-4505, 2002. 10.1063/1.1499754. arXiv:quant-ph/0110143.
 Thomas G. Draper, Samuel A. Kutin, Eric M. Rains, and Krysta M. Svore. A logarithmic-depth quantum carry-lookahead adder. 2004. URL https://arxiv.org/abs/quant-ph/0406142.
 Austin Fowler, Dmitri Maslov, Cody Jones, and Matt Amy. Private correspondence, Aug 2017.
 Austin G. Fowler, Matteo Mariantoni, John M. Martinis, and Andrew N. Cleland. Surface codes: Towards practical large-scale quantum computation. Physical Review A, 86 (3), sep 2012. 10.1103/physreva.86.032324.
 J. M. Gambetta, J. M. Chow, and M. Steffen. Building logical qubits in a superconducting quantum computing system. npj Quantum Information, 3 (2), 2017. 10.1038/s41534-016-0004-0. arXiv:1510.04375.
 Clare Horsman, Austin G Fowler, Simon Devitt, and Rodney Van Meter. Surface code quantum computing by lattice surgery. New Journal of Physics, 14 (12): 123011, 2012. 10.1088/1367-2630/14/12/123011.
 Mark Howard and Earl Campbell. Application of a resource theory for magic states to fault-tolerant quantum computing. Physical review letters, 118 (9): 090501, 2017. 10.1103/PhysRevLett.118.090501.
 V. Lahtinen and J. K. Pachos. A short introduction to topological quantum computation. 10.21468/SciPostPhys.3.3.021. URL https://arxiv.org/abs/1705.04103.
 B. Lekitsch, S. Weidt, A. G. Fowler, K. Mølmer, S. J. Devitt, C. Wunderlich, and W. K. Hensinger. Blueprint for a microwave trapped-ion quantum computer. Science Advances, 3 (2): e1601540, 2017. 10.1126/sciadv.1601540. arXiv:1508.00420.
 R. Raussendorf and J. Harrington. Fault-tolerant quantum computation with high threshold in two dimensions. Phys. Rev. Lett., 98: 190504, 2007. 10.1103/PhysRevLett.98.190504. arXiv:quant-ph/0610082.
 Robert Raussendorf, Jim Harrington, and Kovid Goyal. Topological fault-tolerance in cluster state quantum computation. New Journal of Physics, 9 (6): 199, 2007. 10.1088/1367-2630/9/6/199.
 Malte Schlosser, Sascha Tichelmann, Jens Kruse, and Gerhard Birkl. Scalable architecture for quantum information processing with atoms in optical micro-structures. Quantum Information Processing, 10 (6): 907, 2011. 10.1007/s11128-011-0297-z. 1108.5136.
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