Figure 5.Matter-wave diffraction started in 1930 with diatomic particles,but it didn't gain momentum until the early 1990s.Since then the technique has been extended to progressively larger and more complex molecules;some are depicted here along with their mass in atomic mass units,the number of atoms they comprise,and the year they were first successfully used in interference experiments.To date,a functionalized tetraphenylporphyrin,synthesized by Marcel Mayor and colleagues,is the most massive object for which matter-wave interference has been seen.In the future, bionanomatter such as hemoglobin proteins will likely be studied using matter-wave-enhanced measurements. H He2,Na,I,:Buckminsterfullerene Tetraphenylporphyrin Functionalized Hemoglobin 2 amu,2 atoms 8-254amu, 720 amu,60 atoms 614 amu,78 atoms Tetraphenylporphyrin >60000amu,-10000 atoms (1930) 2 atoms (1999) (2003) 10 123 amu,810 atoms (199495) (2013) Atom gravimeters will be important for envi- equivalence principle,for instance,would be to ronmental monitoring applications:Earthquakes compare matter of vastly different composition or and volcanoes may give telltale warnings in the to systematically explore the mass dependence of form of weak local accelerations.Earthbound and phase shifts.Almost certainly,those studies will satellite-based inertial sensors may permit a more happen in the future. precise determination of the geoid-Earth's gravita- For now,however,atom interferometry contin- tional equipotential surface-and thereby provide ues to lead the way in sensing,because hundreds of climatologists with information about changes of research groups have spent more than three water tables and glaciers. decades on the development of cold and ultracold Quantum gravimeters with a sensitivity of 1 part atom technologies.The development of intense in 10 or better can assist in the prospection for deeply sources of neutral macromolecules and highly effi- buried natural resources.Closer to the surface,small cient detectors is still an open challenge. caves or sewage pipes might be detectable via quan- In my group at the University of Vienna,we've tum gravity gradiometry. chosen to focus our molecular interferometry efforts Atomic inertial sensors are also of interest for on questions that no other experiment could ad- navigation systems.Global positioning systems rely dress with the same precision and scope.On the one on satellite signals,which are inaccessible in deep hand are tests of the linearity of quantum mechanics water and may be jammed by adversaries in the case in the limit of ultrahigh masses.On the other hand of a military conflict.In the future,inertial naviga- is the study of delocalized particles in well-defined tion systems that combine gravitational and rota- fields,which yields information about the particles' tional accelerometers may enable precise position- internal properties.In KDTL and OTIMA interfe- ing by integrating all accelerations along a path rometry,the particles may be atoms,molecules,or Only the occasional correction with an external even clusters of molecules. control signal would be necessary.Many of those Molecular-beam deflection,in which molecules' applications are expected to flourish as soon as internal properties are inferred from changes to their devices become compact and portable. trajectory in an applied external field,is a well- Ultrasensitive atom gravimeters will set new established method in physical chemistry.In con- bounds on deviations from the weak equivalence trast to classical machines,which typically realize principle-the conjecture that an object's freefall molecular beam widths around 100 um,our quan- trajectory is independent of its composition and tum interferometers can create molecular nano- structure-on violations of local Lorentz invariance, patterns with periods as small as 80 nm.Beam shifts on the gravitational redshift,and on the postulated can therefore be seen with more than a thousand- existence of a "fifth force."They may also serve as fold increase in position sensitivity. detectors for low-frequency gravitational waves. In 2007 we used a Talbot-Lau interferometer to Whereas inertial sensing uses atoms as test determine the static polarizability of the fullerenes masses to measure external fields,precision meas- carbon-60 and carbon-70.With KDTL interferome- urements of the photon recoil in a Raman beam- try,it is now possible to study the influence of per- splitter allow extraction of the ratio of h to atomic manent and even dynamic electric dipole moments mass.4 That ratio,along with precise mass meas- in a large variety of organic molecules.5 It will be urements,yielded the fine structure constant possible to explore the magnetic world of molecules a1=137.035 999 037 with a relative uncertainty of and clusters:aromaticity,magnetic dipole moments, 6.6×10-10. and,eventually,phase transitions in clusters. Most recently we have explored the possibility Molecules as quantum sensors of using molecule interferometers to measure ab- In principle,a molecule interferometer can detect solute optical absorption cross sections:The recoil both inertial forces and relativistic effects,just as an imparted on each molecule due to the absorption of atom interferometer can.An interesting test of the a single photon is sufficient to noticeably shift the www.physicstoday.org May 2014 Physics Today 35www.physicstoday.org May 2014 Physics Today 35 Atom gravimeters will be important for envi￾ronmental monitoring applications: Earthquakes and volcanoes may give telltale warnings in the form of weak local accelerations. Earthbound and satellite- based inertial sensors may permit a more precise determination of the geoid—Earth’s gravita￾tional equipotential surface—and thereby provide climatologists with information about changes of water tables and glaciers. Quantum gravimeters with a sensitivity of 1 part in 108 or better can assist in the prospection for deeply buried natural resources. Closer to the surface, small caves or sewage pipes might be detectable via quan￾tum gravity gradiometry. Atomic inertial sensors are also of interest for navigation systems. Global positioning systems rely on satellite signals, which are inaccessible in deep water and may be jammed by adversaries in the case of a military conflict. In the future, inertial naviga￾tion systems that combine gravitational and rota￾tional accelerometers may enable precise position￾ing by integrating all accelerations along a path. Only the occasional correction with an external control signal would be necessary. Many of those applications are expected to flourish as soon as devices become compact and portable. Ultrasensitive atom gravimeters will set new bounds on deviations from the weak equivalence principle—the conjecture that an object’s freefall trajectory is independent of its composition and structure—on violations of local Lorentz invariance, on the gravitational redshift, and on the postulated existence of a “fifth force.” They may also serve as detectors for low- frequency gravitational waves. Whereas inertial sensing uses atoms as test masses to measure external fields, precision meas￾urements of the photon recoil in a Raman beam - splitter allow extraction of the ratio of h to atomic mass.14 That ratio, along with precise mass meas - urements, yielded the fine structure constant α−1 = 137.035 999 037 with a relative uncertainty of 6.6 × 10−10. Molecules as quantum sensors In principle, a molecule interferometer can detect both inertial forces and relativistic effects, just as an atom interferometer can. An interesting test of the equivalence principle, for instance, would be to compare matter of vastly different composition or to systematically explore the mass dependence of phase shifts. Almost certainly, those studies will happen in the future. For now, however, atom interferometry contin￾ues to lead the way in sensing, because hundreds of research groups have spent more than three decades on the development of cold and ultracold atom technologies. The development of intense sources of neutral macromolecules and highly effi￾cient detectors is still an open challenge. In my group at the University of Vienna, we’ve chosen to focus our molecular interferometry efforts on questions that no other experiment could ad￾dress with the same precision and scope. On the one hand are tests of the linearity of quantum mechanics in the limit of ultrahigh masses. On the other hand is the study of delocalized particles in well- defined fields, which yields information about the particles’ internal properties. In KDTL and OTIMA interfe - rometry, the particles may be atoms, molecules, or even clusters of molecules. Molecular- beam deflection, in which molecules’ internal properties are inferred from changes to their trajectory in an applied external field, is a well- established method in physical chemistry. In con￾trast to classical machines, which typically realize molecular beam widths around 100 μm, our quan￾tum interferometers can create molecular nano - patterns with periods as small as 80 nm. Beam shifts can therefore be seen with more than a thousand￾fold increase in position sensitivity. In 2007 we used a Talbot–Lau interferometer to determine the static polarizability of the fullerenes carbon-60 and carbon-70. With KDTL interferome￾try, it is now possible to study the influence of per￾manent and even dynamic electric dipole moments in a large variety of organic molecules.5 It will be possible to explore the magnetic world of molecules and clusters: aromaticity, magnetic dipole moments, and, eventually, phase transitions in clusters. Most recently we have explored the possibility of using molecule interferometers to measure ab￾solute optical absorption cross sections: The recoil imparted on each molecule due to the absorption of a single photon is sufficient to noticeably shift the Figure 5. Matter- wave diffraction started in 1930 with diatomic particles, but it didn’t gain momentum until the early 1990s. Since then the technique has been extended to progressively larger and more complex molecules; some are depicted here along with their mass in atomic mass units, the number of atoms they comprise, and the year they were first successfully used in interference experiments. To date, a functionalized tetraphenylporphyrin, synthesized by Marcel Mayor and colleagues, is the most massive object for which matter- wave interference has been seen. In the future, bionanomatter such as hemoglobin proteins will likely be studied using matter- wave-enhanced measurements. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 202.120.2.30 On: Thu, 01 May 2014 23:26:12