Quantum Information Processing as told by: David G. Cory Department of Nuclear Science & Engineering Massachusetts Institute of Technology Neutron Interferometry Dmitry Pushin Physics, MIT

Dr. Sekhar Ramanathan Dr. Timothy Havel Professor Seth Lloyd Dr. Sergio Valenzuela Dr. Will Oliver Dr. John Bernard Dr. M. Arif, NIST University of Waterloo Professor Joseph Emerson Professor Raymond Laflamme Dr. Jonanthan Baugh

Dr. Timothy Havel Professor Seth Lloyd Dr. Sekhar Ramanathan Dr. Joseph Emerson Paola Cappellaro Michael Henry Jonathan Hodges Suddhasattwa Sinha Jamie Yang

Planck - photons Bell - locality tests Bohr - old QT, interpretation Dirac - relativistic wave-equation Einstein Heisenberg - new QT Schrödinger - wave equation Landauer - information is physical

Old QT New QT TestsQIP Haroche Aspect Zeilinger

Quantum mechanics permits information processing beyond the classical limit These new possibilities are Macroscopic Quantum Coherence

Neutron interferometry an example of macroscopic quantum coherence 3-blade, interferometer Size ~ 10 cm Neutrons 2.1 Å ~ 1800 m/s ~ 50 µs / 10 cm 1 neutron every 0.35 s

Neutron interferometry an example of macroscopic quantum coherence Bragg scattering Each neutron is coherently spread over two paths

Neutron interferometry an example of macroscopic quantum coherence Ignore the beam that is scattered out of the interferometer No information lost. The transmitted and reflected beams carry the same information,

Neutron interferometry an example of macroscopic quantum coherence Third blade recombines the beams and allows them to interfere.

Neutron interferometry an example of macroscopic quantum coherence t - transmitted r - reflected

Neutron interferometry an example of macroscopic quantum coherence Measure the neutron Intensity. In this case that is the number of neutrons per unit time.

Interference A: B: |path I  |path II  C: D: 3 He detectors H-beam O-beam path I path II ABCD O-beam: H-beam:

Neutron interferometry an example of macroscopic quantum coherence Clothier et al, (1991) PRA 44, 5357 Neutons/ 3 min phase

Neutron interferometry an example of macroscopic quantum coherence A simple example of probability amplitudes. Set   

Coherent Neutron Imaging

Spatially encoding of the neutron beam 3 He detector position sensitive detector wedge Neutron beam By spatially encoding beam we are introducing a new degree of freedom. By tracing this degree we can: measure spatial properties of materials (softmatter) use it as controlled decoherence in QIP

Coherent Neutron Imaging Vary k to collect a complete set of Fourier components. The resolution depends on S/N not the detector.

Spatial encoding - No sample - Step-like sample The fit is to the known sample geometry, parameters are step location and size. Notice that each point is 50 minutes of averaging.

Spin Polarized Neutrons Polarizer Analyzer Detector π π/2 += not

Interference and spin A: B: |path I  |path II  C: D: H-beam O-beam path I path II ABCD O-beam: H-beam:   /2 Polarizer Analyzer += not

Spin based phase grating

Coherence Measurements Fussed Silica Wedges used to move vertically one beam with respect to another Phase Flag Neutron beam To the detectors Contrast measurements directly yields the coherence function A neutron interferometer is a macroscopic quantum coherence device, we will measure the coherence length of the neutrons wave-function. Radius of neutron = 0.7 fm

Coherent neutron scattering 3-blade interferometer with prisms to vertically shift the beam. Adjust phase for only O-beam. Add second interferometer. First example of coherent neutron wave-funtion over two interferometers

When will we have a neutron Interferometer at MIT? Sample Top View Neutron wave function coherently split by Bragg diffraction. 3 He detectors  Phase Shifter  H-beam O-beam path I path II 10 cm

Each crystal blade acts as a beam splitter.

Neutron interferometry with vibrations Vibrations change the momentum of the n and thus the Bragg angle. Note, the two paths change in opposite directions. Even low frequency vibrations are deadly.

Neutron interferometry with vibrations Low frequency vibrations are OK. Nointerference

When will we have a neutron Interferometer at MIT? Multiple interferometers for controlling neutron information. Multiple interferometers for controlling neutron information. Multiple paths to code for errors. Multiple paths to code for errors. Spin dependent measurements to correct for momentum spread. Spin dependent measurements to correct for momentum spread.

Stern-Gerlach (details) π/2 π Gradient magnets AnalyzerPolarizer Sample Detector II IIIIV VVI where I I II III IV V VI

J. C. Gore C. Breen S. Kumaresan N. Seiberlich J. S. Hodges K. Edmonds J. Yang Decoherence Free Subspace Construction and Implementation of Logic Gates on two Spins Quantum and Classical Channel 2003 A. Gorshkov M. Henry H H () n H Journal of Magnetic Resonance Concepts in Magnetic Resonance New Journal of Physics Physical Reviews A Center for Materials Science and Engineering Summer Students (NSF) Physical Reviews A 2004 D. Khanal EIT

Dr. Timothy Havel Professor Seth Lloyd Dr. Sekhar Ramanathan Dr. Joseph Emerson Dr. Grum Teklemariam Dr. Greg Boutis Nicolas Boulant Paola Cappellaro Zhiying (Debra) Chen Hyung Joon Cho Daniel Greenbaum Michael Henry Jonathan Hodges Suddhasattwa Sinha Jamie Yang